Symposium PM5 : Hierarchical, Hybrid and Roll-to-Roll Manufacturing for Device Applications

Meanwhile R2R-nanoimprint lithography has proven as a very powerful tool to realize hierarchical structures on large areas of flexible substrates at medium to high throughput. Such roller-imprinted microstructures with nanoscale features are essential for many applications based on biomimicry and fluid dynamics. On the one hand hierarchical structures can be utilized to control the drag resistance of objects moving fast in fluids and on the other hand the wettability of fluids on patterned surfaces with hierarchical structures can be tuned from superhydrophobic to spontaneous wettability. The latter is a property that can be exploited for ink and fluid transport, microfluidics, and multilevel patterning. This paper introduces R2R-UV-Nanoimprint Lithography for the combined micro- and nanopatterning of proprietary UV-curable liquid resist layers thus aiming for the creation of large-area film surfaces with controlled wettability. We demonstrate the fast and reliable fabrication of microfluidic devices for lab-on-chip devices and embedded metal patterns and verify our results by simulation and quantitative measurements of the fluid dynamics. Moreover, the long-term stability of the R2R-UV-NIL process w.r.t. durability of the applied polymer and Ni stamps and of the resist materials and structures will be discussed. Finally, new findings about pattern reproduction fidelity and UV-induced polymer shrinkage in thiol-ene imprint resist systems will be presented both for flat and roller-based imprinting.

Nanoimprint lithography has perhaps the greatest potential of any lithographic method to incorporate the extraordinary properties of nanostructured materials into mass-produced devices. Further, the use of sacrificial templates for nanoimprint greatly expands the capability of the method particularly with regards to maximum aspect ratio. Here, we demonstrate the ability for the sacrificial imprint method using zinc oxide nanorods developed for hierarchical forming of bulk metallic glass to be extended to the high throughput production of porous polymer membranes. It is established that such structures can be grown cheaply and quickly with tunable morphologies on a wide variety of substrates out of solution, which we exploit to generate the nanoscale imprint features through this bottom-up approach. In this technique, rods grown on one substrate are transferred to a film through a combination of nanoimprint and nanotransfer printing. Since the oxide materials are sacrificial and regrowable, issues of detachment that complicate conventional nanoimprint are mitigated. Through etching the oxide, we are left with a dense array of pores in the transferred material. By using a supported polymer film thinner than the oxide rods, these films become perforated membranes. In this study, we employ the technique to produce films with sub-100 nm pores and pore aspect ratios exceeding 5 for the application of support layers for osmosis membranes produced by layer-by-layer processing. Due to the flexibility of the sacrificial imprint paradigm, films produced in this way are highly scalable to large areas or even roll-to-roll processing.

New added-value functionalities are increasingly demanded on polymer components and products for many different applications, while surface texturing technologies at the nanoscale have emerged as one of the natural responses to integrate more capacities to current parts, ranging from enhanced mechanical properties and tribological behaviours, to light and fluids interaction control.
We discuss how to utilize advanced nanoimprint based manufacturing processes to mass replicate nano metric scale structures. We debate the use of roll to roll nanoimprint & injection moulding technologies to produce large area, high volume nano enabled products, components and surfaces with tailored functionalities.

Roll-to-Roll-UV-nanoimprint lithography (R2R-UV-NIL) enables high resolution large area patterning of flexible substrates and is therefore of increasing industrial interest.
We have set up a custom-made R2R-UV-NIL pilot machine which is able to convert 10 inch wide web with velocities of up to 30 m/min. In addition, we have developed self-replicable UV-curable resins with tunable surface energy and Young’s modulus for UV-imprint material as well as for polymer working stamp manufacturing.
Now we have designed test patterns for the evaluation of the impact of structure shape, critical dimension, pitch, depth, side wall angle and orientation relative to the web movement onto the imprint fidelity and working stamp life time.
This test design contains line/space-patterns and crosshatch lines with various pitches and orientations as well as square dots with various pitches and isolated crossed lines. Female (recessed structures) silicon masters of this design have been used with critical dimensions of
CD = 200 nm, 400 nm, 800 nm and 1600 nm, and structure depths of d = 500 nm and 1000 nm - all with vertical as well as slightly inclined (~ 80°) side walls.
This entire master pattern set has been transferred onto single male (protruding structures) R2R polymer working shims, which in turn have been used for R2R-UV-NIL runs of several hundred meters.
In combination with R2R-process parameters such as web speed and UV-power the imprint fidelity and its durability - i.e. polymer working stamp lifetime - of the various test patterns have been compared.
This study is intended as a first step towards establishing of design rules and developing of nanoimprint proximity correction strategies for industrial R2R-UV-NIL processes using polymer working stamps.

The fabrication and advanced function of large area biomimetic superhydrophobic surfaces (SHS) and slippery lubricant infused porous surfaces (SLIPS) are reported. The use of roll-to-roll nanoimprinting techniques enabled the continuous fabrication of SHS and SLIPS based on hierarchically wrinkled surfaces. Perfluoropolyether (PFPE) hybrid molds were used as flexible molds for roll-to-roll imprinting into a newly designed thiol-ene based photopolymer resin coated on flexible polyethylene terephthalate (PET) films. The patterned surfaces exhibit feasible superhydrophobicity with a water contact angle around 160° without any further surface modification. The SHS can be easily converted into SLIPS by roll-to-roll coating of a fluorinated lubricant, and these surfaces have outstanding repellence to a variety of liquids. Furthermore, both SHS and SLIPS display anti-biofouling properties when challenged with Escherichia coli K12. The current report describes the transformation of artificial biomimetic structures from small, lab scale coupons to low cost, large area platforms.

Mechanical energy harvesting still remains an emerging technology since the late 90’s. The interest in lead-free piezoelectric materials has significantly increased during the past few years for their environmental-friendly properties. In this work, a large scale fabrication of an efficient piezoelectric nanogenerator is demonstrated. A top-down approach is used, compared to the usual bottom-up ZnO nanowires. The fabrication combines Nano-Imprint Lithography (NIL) and low-temperature (<80°C) Atomic Layer Deposition (ALD). The NIL process leads to a PMMA regular array of truncated conical holes of 2 μm in depth. The conical shape of the stamp allows for reaching a high aspect ratio of 10. These holes are then filled with 150 nm-thick polycrystalline ZnO film by low-temperature ALD. A p-n junction is created by adding 100 nm-thick PEDOT by plasma radicals assisted polymerization via chemical vapour deposition¹. A functional device is demonstrated on a flexible substrate with 4x4 mm² active surface. We have measured an output voltage of 200 mV corresponding to an effective transverse piezoelectric coefficient e_31eff of -0.45C/m². Voltage output, effective transverse piezoelectric coefficient, generated power will be reported for a 5x5 cm² device.


[1] Pistillo et al., J. Mater. Chem. C, 2016

Block copolymer (BCP) self-assembly has emerged as an enabling technology for large scale fabrication of nanoscale patterns with potential impact on flow membranes, photonic crystals, magnetic storage media, and electronic devices. However, adopting this bottom-up self-assembly approach for nanoscale lithography requires developing techniques for transferring the BCP pattern into functional materials such as metals. Typically, BCP pattern transfer is achieved by either chemical modification, or removal of one of the blocks and use of the other block as a mask for deposition, liftoff, and/or etching. These multistep processes add to the complexity and cost of fabrication, pose restrictions on the type of substrates to be used, and may cause degradation, as well as size/shape errors. Hence, alternative scalable processes for pattern transfer are needed. In this work, we developed a templated metal dewetting process for creating large-area arrays of gold nanoparticles guided by a BCP pattern. Solid-state dewetting of thin films is a process by which a population of small nanoscale particles are created, typically on flat surfaces, by thermal annealing. Here, we use a pattern of raised posts as a template for directing the dewetting process. BCP patterns are created by solvent annealing of poly(styrene-block-dimethylsiloxane) (PS-b-PDMS) with molecular weight of 56.1 kg/mol (f_PDMS = 17.1%) using toluene to achieve a hexagonal array of PDMS spheres in a PS matrix. After CF₄ etching of the topmost PDMS layer and O₂ reactive ion etching (RIE) for the removal of the PS matrix and the oxidation of PDMS, a hexagonal array of 20 nm diameter posts of oxidized PDMS is left on the sample with 20 nm spacings between posts. A 5-nm-thick film of gold is then deposited on top of the template by electron beam evaporation, and a rapid thermal processing (RTP) system is used for annealing. Results show that a rapid temperature ramp to 400°C in 30 second with 1 second dwell time leads to the formation of one-dimensional fingers on the surface that pinch-off, forming nanoparticles if the dwell time is extended to 30 seconds. This break-up of the film is possible owing to the atomic mobility at high temperature, which drives atomic diffusion in order to minimize surface energy. Our BCP-templated dewetting process enables scalable patterning of high density quasi-ordered metal nanoparticles, with monodisperse size distributions compared to non-templated dewetting. The packing density of nanoparticles is higher than that of the original array of posts owing to the agglomeration of nanoparticles both on top of the posts and on the surface surrounding the posts. Hence, this approach can be employed for manufacturing arrays of functional nanoparticles such as plasmonic structures, or for creating arrays of catalyst nanoparticles for substrate-bound catalytic nanotube/nanowire synthesis.

In this work, high voltage capacitors are used as a model system for investigating template-free 3D printing technology because of their inherently multimaterial structure and low defect tolerance. PMMA and PVDF-HFP inks were printed using solution-cast direct write and compared against more the traditional film casting techniques of spin casting and flow coating. The printed films from inks based on these polymers displayed programmable thicknesses (2 µm to 10 µm) and comparable dielectric breakdown strength to films deposited using the more traditional lab-scale casting procedures as well as commercially used dielectric films. Conductive inks were then developed based on each of the dielectric systems and used to make all-printed high voltage capacitors. Single- and multi-layer capacitors are printed in 3D with capacitances as large as 326 pF (at 1 kHz) and breakdown voltages over 1,000 V, which is a significant step towards template-free, 3D printing of high performance electronics for multifunctional rapid prototyping.

The ability to pattern materials at the nanoscale can enable a variety of applications in areas such as nanoelectronics, optical metamaterials, and emerging applications in nanomedicine. This presentation will discuss recent progress in cost-effective roll-to-roll (R2R) nanoscale patterning based on imprint lithography. The presentation will also discuss the complementary R2R technologies such as nanoscale thin film coatings using slot die coating techniques, R2R sputtering and e-beam evaporation, and R2R reactive ion etching. The speaker will discuss ongoing efforts at the NASCENT Center at the University of Texas at Austin to bring silicon IC grade nanofabrication to the world of R2R processing, including contamination control, nanoscale metrology and yield management strategies.

If a reliable and cost-effective R2R nanofabrication capability can be established, there are major potential applications in areas such as photonic devices for displays, and size and shape controlled nanocarriers for targeted drug delivery. This presentation will discuss the performance and cost metrics associated with display photonics and nanocarrier drug delivery applications, and present a technology gap analysis between these application metrics and the current state-of-the-art in R2R nanofabrication.

Smart labels and wearable biosensors based on thin-film transistor (TFT) devices fabricated on thin plastic film substrates with various printing processes have been attracting significant attention in research and development. In particular, TFT devices based on organic semiconductors (OSC) can be fabricated at low temperatures and are more compatible with printing methods than inorganic semiconductors. Here, we will report briefly on printable materials, printed OTFT devices and their application to TFT arrays and integrated circuits.
Silver (Ag) nanoparticle inks have become important materials for the fabrication of electrode and interconnect layers in printed electronics. Accordingly, we developed a Ag nanoparticle ink that was optimized for organic TFT applications. Finely patterned Ag lines with line widths of 25 mm were fabricated by inkjet printing and sintered at temperatures lower than those reported for other Ag nanoparticle inks. A low resistivity of less than 10 mWcm could be obtained in the printed lines by thermal sintering at 120°C or photonic sintering for 1msec. We adopted newly developed p-type OSC material based on dithienobenzodithiophene derivative (DTBDT), which is soluble in common organic solvents and highly crystalline. High mobility over 3 cm²/Vs and high on/off current ratio of 10⁷ were obtained in a typical bottom-contact top-gate OTFT device. N-type OSC material, TU series, based on benzobisthiadiazole moiety was also developed. A mobility of 2 cm²/Vs was demonstrated in a top-contact bottom gate device structure.

Inkjet printing, nozzle dispensing and reverse-offset printing methods were largely employed in forming the electrode, bank and OSC layers, resulting in fully-printed OTFT devices. Printed OTFT arrays (30x30) were successfully fabricated employing DTBDT on plastic film substrates. By optimizing the semiconducting layer crystal growth, excellent p-type electrical performance with a high mobility of 1.9 cm²/Vs and high on/off current ratios over 10⁷ were achieved. Exceptional uniformities of device characteristics were also observed within in the array. Ultra-thin OTFT devices can also be fabricated using ultra-thin Parylene-C films. The resulting ultra-thin printed OTFT devices and inverter circuits were extremely lightweight, flexible and compressible.
One of the important applications of OTFT devices is integrated circuits for RFID and microprocessor. We successfully fabricated pseudo-CMOS inverters using the p-type OTFTs, as well as NAND logic gates that exhibited ideal characteristics at a low voltage operation. Very high gains over 250 were obtained in the printed pseudo-CMOS inverters. Of course, real CMOS inverter using both p-type and n-type OSC materials are significantly important for the integrated circuit fabrication. We proposed stacked TFT structure for the CMOS inverter and fabricated using our n-type OSC material (TU-3) and commonly used p-type OSC material (diF-TES-ADT). Good switching characteristics were observed and a high gain was obtained at an operating voltage of 10 V. Based on this CMOS inverter a three –stage ring oscillator and D-flip flop circuits were also fabricated on a ultra-thin substrate based on Parylene film. In order to realize very shot-channel OTFT devices and their integrated circuits we have employed the reverse offset printing method and obtained good characteristics in the printed CMOS inverters.

Integrating ultra-miniaturized high-performance devices onto non-native substrates enables new kinds of products with desirable functionalities and cost structures that are inaccessible by conventional means. Micro assembly technologies are the practical ways to make such micro-scale hybrid combinations possible. Micro transfer printing technology (µTP) is a widely-demonstrated form of micro assembly, having demonstrated applicability in optical communications, magnetic storage, photovoltaics, and displays. The common value proposition of µTP in all of these applications is to provide a product that uses the most advantageous semiconductor devices and has the most desirable form factor.

Fully printable nanowire (NW) transistor devices present a significant challenge for the integration of semiconducting NW components and the electrodes. The precise positioning and orientation of solution processed nanowires, together with an efficient micron-scale resolution electrodes printing, require self-assembly and self-alignment deposition techniques. Additionally, an industry scalable NW growth methods should underpin printed electronics (PE) device fabrication.
In this work we demonstrate, perhaps, the smallest printed NW field-effect transistors (FET) that fit on a cross section of a human hair. The silicon NWs (SiNWs) placement is accomplished by a variety of methods, including spray-deposition, dip-coating, roll-coating and dielectrophoresis (DEP). Electrodes are fabricated by precision ink-jet printing (IJP) of metal nanoparticle (MNP) inks, coupled with self-dewetting approach. The electrodes gap, achievable with IJP, was controlled by varying jetting parameters, substrate surface energy and de-wetting characteristics to produce structures with variable gap lengths, from sub-micron to several microns, obtained with silver inks. The technique did not require any pre-structuring of the substrate.
To demonstrate larger-channel-width printable FETs, we have developed a method for one-step NW positioning, alignment, purification and selection of Supercritical Fluid-Liquid-Solid (SFLS) grown SiNWs. Currently, SFLS is one of very few techniques, which can deliver scalable NW synthesis with up to few kg per day yield. Main challenge associated with SFLS growth is the heterogeneous nature of produced NWs, with various levels of lengths, conductivities and crystalline qualities. Using DEP and impedance spectroscopy we demonstrate the selection mechanism at high signal frequencies (5-20 MHz) for isolating NWs with the highest conductivity and lowest defect density, directly confirmed by FET and conductive-AFM data. This scalable one-step solution process offers the direct selection, collection and ordered assembly of SiNWs into large area arrays with desired electrical properties and lengths of NWs, and controlled number of NWs in the device channel area ranging from a few NWs to hundreds per device. The NW FET devices demonstrate excellent performance, with up to mA on-current at 10V, steep sub-threshold swing, charge-carrier mobility of 50 cm²/Vs, and near-zero hysteresis. The proposed method is fully compatible with plastic and PE approaches and can be applied to any other type of nano-materials for a wide range of device applications, including chemical and biological sensing. Finally, SiNW FETs were operated as gas sensors and have demonstrated highly sensitive response to volatile organic compounds, such as benzene.
In summary, we demonstrate a solution-based methodology for the accurate deposition and selection of semiconducting NWs and controllable few-micron gap size fabrication of FET electrodes through a precision IJP of MNP inks.

With the burgeoning development of the internet of everything (IoE), research involving high-speed, low cost, and large volume electronics manufacturing is highly attractive. Hybrid electronic systems, involving flexible printed and traditional silicon components, present early enablers for the large scale fabrication of printed electronics with a high level of computational power. With this possibility, there may be a way to produce the trillions of sensors needed for the fruition of the IoE.
Of particular interest, is the ease at which rotary screen printing can be utilized in the roll-to-roll (R2R) fabrication process of flexible electronics. However, there are challenges to be overcome regarding the printed line resolution and hybrid integration utilizing high speed rotary screen printed backplanes. Our study, focused on R2R screen printed high density interconnects on PET, utilizing commercially available silver pastes. To evaluate the hybrid integration, we designed symmetrical daisy chain bare dies with 80 pads and varying pitch sizes of 150, 175, and 200 µm. Initially we investigated the use of anisotropically conductive adhesives and the comparison of native and gold stud bumped chips. Subsequently, we investigated the optimization of the printed traces via calendaring in an effort to improve the flip-chip attachment. The R2R calendaring was used to increase the line height uniformity of the printed traces and decrease the interconnects surface roughness.

Over the last decade, roll-to-roll (R2R) printing has been pursued with the expectation of developing a commercially viable, high throughput technology to manufacture flexible, disposable and inexpensive printed electronics. However, in recent years, pessimism has emerged due to the barriers faced when attempting to fabricate and integrate thin film transistors (TFT) using R2R printing. In this presentation, we will report for the first time, TFT based active matrix backplanes with 40 ppi (pixel per inch) resolution obtained via a fully R2R gravure printing process with semiconducting inks, respectively formulated by single walled carbon nanotubes (SWCNT) and Poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT). Using respectively single walled carbon nanotubes (SWCNT) and PBTTT as the semiconducting layer and poly(ethylene terephthalate) (PET) as the substrate we obtained about a 89 % device yield in 15 x 0.25 m² of PET roll and extracted the scalability factors needed for a feasible manufacturing process. Smart sensor arrays or digital paper (signage) can be obtained by laminating a pressure sensitive rubber or e-paper sheet to the TFT backplane. The R2R gravure printing process we have developed addresses several barriers in the fabrication and integration of printed TFTs, circumventing or surmounting challenges associated with the alignment of source-drain and gate electrodes, threshold voltage (V_th) shift, and overall device yield, proving that R2R printing is indeed a viable advanced manufacturing technology that can enable high throughput production of flexible, disposable and cutting edge printed electronics.

Transparent conductive electrodes are key components of many electronic devices, such as light-emitting diodes, touchscreen displays, and solar cells. In spite of the continued use of indium tin oxide (ITO) in these applications, there remains a strong need for new transparent electrode materials due to the limited material supply and mechanical fragility of ITO. Recently, there has been great interest in using conductive polymers, carbon nanomaterials, metal nanowires, and patterned grids as alternative materials for transparent conductive films. For applications where surface roughness is not critical, in particular, patterned metal grids can be a superior alternative providing high transparency and low sheet resistance. However, current manufacturing techniques, including photolithography and micro-contact printing, require multiple-step processing. On the other hand, direct printing technologies are more scalable and cost-effective yet are limited by the spatial resolution that determines the minimum grid line width.
We demonstrate flexographic printing of transparent silver electrodes with micrometer resolution using nanoporous stamps. The nanoporous stamps comprise patterned vertically-aligned coated carbon nanotubes (CNTs) conformally coated with an ultrathin low surface energy polymer via initiated chemical vapor deposition (iCVD). These microstructures are highly porous (>90% porosity), wettable with colloidal inks but mechanically-durable against capillary shrinkage due to the iCVD coating, and yet compliant enough to enable conformal contact during flexoprinting. As a result, the stamps enable direct printing of a silver nanoparticle ink with micrometer lateral resolution on both rigid and flexible substrates. Using this approach, thin (~100 nm) silver transparent conductive films are printed directly using CNT ‘honeycomb’ stamps; these honeycomb patterns have a hexagonally arranged hole pattern with diameter of 5-22 μm and center-to-center spacing of 8-25 μm (open area of 47-94 %). After thermal annealing, the printed silver honeycomb patterns exhibit high transparency (> 90%) over the 200-800 nm wavelength range and low sheet resistance of <10 Ω/sq. The thickness of the printed ink layer is controlled by the contact pressure and stamp design; because the nanoporous stamp directly transfers a colloidal ink with high loading, the printed feature remains uniform during subsequent evaporation of the solvent. Using a custom-built precision plate-to-roll printing apparatus, we fabricate a variety of transparent electrode designs at printing speeds of up to 0.2 m/s, explore design rules and process limits for optimizing conductivity and transparency, and discuss use of this process to pattern other electronic materials.

Typically, optoelectrical performance of thin-film based transparent conducting electrodes (TCEs) such as indium tin oxide (ITO) is inherently limited by the trade-off between the transmittance and sheet resistance. Previous studies on periodic nanopatterned metal-based TCEs have shown that high-aspect-ratio metal nanostructures can relieve the trade-off.^{1, 2} However, fabrication of such high-aspect-ratio metal nanostructures is still challenging with conventional top-down approaches.
In this report, we fabricate periodic Ag nanogrid electrodes by assembling silver nanoparticles (AgNPs) along patterned nanogrid templates.³ The AgNPs are selectively assembled into the trenches by capillary forces induced at the receding meniscus while the three-phase (air-suspension-substrate) contact line of the AgNP suspension is dragged over the patterned nanogrid template (width = 150 nm and height = 450 nm). For the uniform and selective assembly of AgNPs, contact angle of the meniscus, concentration and evaporation rate of AgNP suspension are carefully controlled. High junction resistances between nanoparticles is effectively reduced by photochemical welding and post-annealing. Our high-aspect-ratio silver nanogrids have an average sheet resistance of 15.2 Ω/sq and optical transmittance of 85.4 %.⁴ The speed of fabrication by capillary assembly is significantly improved by controlling the internal flow of nanoparticle suspension, from a few μm/s to 220 μm/s.

1. P. B. Catrysse and S. H. Fan, Nano Lett., 2010, 10, 2944-2949.
2. J. V. van de Groep, P. Spinelli and A. Polman, Nano Lett., 2012, 12, 3138-3144.
3. T. Kraus, L. Malaquin, H. Schmid, W. Riess, N. D. Spencer and H. Wolf, Nat. Nanotechnol., 2007, 2, 570-576.
4. J. Kang, C.-G. Park, S.-H. Lee, C. Cho, D.-G. Choi and J.-Y. Lee, Nanoscale, 2016, DOI: 10.1039/c6nr01896c.

Cu nanowire (NW)-based flexible transparent conducting electrode (FTCE) has been the focus of recent research for a wide range of next-generation electronic devices such as flexible optoelectronic devices, wearable devices, and electronic skins because of its numerous merits such as low material cost, excellent optoelectrical properties, large-scale solution processability, and outstanding mechanical flexibility. Therefore, many researchers have developed facile synthesis approaches to produce Cu NWs in large quantities, methodologies to prevent Cu oxidation, and various post-welding processes to reduce the contact resistance between Cu NWs under ambient atmosphere. However, despite these significant advancements, the widespread use of Cu NW-based FTCEs is still hindered by several issues such as the absence of effective patterning process for them. In this research, we firstly explored simple continuous patterning of Cu NW FTCEs via selective intense pulsed light (IPL) irradiation and a roll-to-roll (R2R) wiping process. In the selective IPL-irradiated Cu NW film, irradiated NWs could not be easily removed from the substrate owing to the strong adhesion developed as they self-nanoembed into the underlying polymer substrate, whereas non-irradiated NWs could be simply eliminated. A custom-built, R2R-based wiping apparatus was employed to remove out non-irradiated NWs continuously, showing that the continuous patterning of Cu NW FTCEs could be possible. In addition, the variations in microscale pattern size by altering IPL process parameters/the mask aperture sizes were investigated and possible factors affecting on developed pattern size were meticulously examined. Finally, to verify the applicability of the patterned Cu NW FTCEs, a phosphorescent organic light emitting diode (PhOLED) and a flexible transparent conductive heater (TCH) were fabricated. The resulting OLED device exhibited the highest efficiencies ever achieved without light-outcoupling structures, and the TCH constructed on the Cu NW FTCEs showed stable heating operation under bending at radii ranging from 10 mm to 30 mm. We believe that this work is a notable step forward in facilitating the practical use of Cu NW FTCEs in various flexible electronic devices.

Xue-Peng Zhan¹, Zhen-Yu Zhang¹, Ming Xu¹, Huai-Liang Xu¹, Hong-Bo Sun^1,2
1State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130023, China
²College of Physics, Jilin University, 119 Jiefang Road, Changchun 130012, China
[email protected], [email protected]

The whispering-gallery (WG) mode microcavity has been paid enormous attentions with the small mode volume and high quality (Q) factor. To overcome the low collection efficiency of the isotropic lasing, deformed microcavity has been proposed to break the rotational symmetry WG shape. With the intrinsic 3-dimensional (3D) prototyping capability with nano-scale spatial resolution, femtosecond laser direct writing (FLDW) has shown its versatility in fabricating various of microsystems. We fabricate of a 3D dye-doped spiral-shaped SU8 microcavity by FLDW via two-photon polymerization. This spiral microcavity with a pillar beneath supports highly directional emission with a Q factor of 1600 and a low lasing threshold. Numerical simulation reveals that clockwise propagating high-Q WG like modes may couple to the counter-clockwise modes and give the directional output. Due to the scattering at the notch section, such high-Q modes exhibit strong far field intensity distribution at 0 degree. Furthermore, a metal-coated hemisphere microcavity is realized by a simple self-assembled process. A film of Teflon materials reducing the surface energy was spin-coated on the substrate. The hemisphere was formed on the hydrophobic surface with the contact angle of 83° and roughness of 0.83 nm. Then it was thermally evaporated with a film of silver on the surface. Plasmon-photon hybrid modes are produced in the metallic microcavity and the lasing wavelength exhibits a blue shift when compared with no-metal cavities. Simulation shows that the blue shift originates from the redistribution of the electric-field intensity. Because the precise 3D fabrication capability of FLDW and the good compatibility of polymer to other materials, the realization of the active unidirectional polymer lasers provides an important step to the functional integrated organic optoelectronic devices. With the flexible and feasible self-assembled process, the high-Q silver-coated hemisphere microcavity provides a promising candidate for fundamental investigation of SPP and WG photon mode interaction.

Referencees
[1] Xue-Peng Zhan, et al. IEEE Photonics Technology Letters, 27, 3, (2015), 311-314.
[2] Xue-Peng Zhan, et al. IEEE Photonics Technology Letters, 28, 3, (2016), 351-354.

Thin films formed of polymer chains densely end-grafted to a surface are known as polymer brushes. The vast range of chemistries and interesting fundamental properties of polymer brushes has led to emerging applications in diverse fields such as biomedicine, microelectronics, photovoltaics and sensing. Patterned polymer brushes are finding application in areas such as directing cell growth, “gecko-mimetic” switchable adhesion, etch resists and photonic based sensors, however no universal and accessible technique capable for the rapid iteration of high resolution patterns (below 1 µm) over large areas currently exists.

Here we report the high-resolution deposition of polyelectrolyte macroinitiators using electrohydrodynamic printing and subsequent polymer brush growth using SI-ARGET-ATRP. We go on to demonstrate for the first time a controlled sub-micron patterning phenomena through a fundamental understanding of formulation interactions in the drying process. It has been found that with the addition of either an appropriately like charged polyelectrolyte homopolymer or through careful control of ionic strength that deposition of macroinitiator can be directed and defined at the sub-micron scale. As a result patterning of polymer brushes down to ca. 200 nm is reported. We present a possible mechanistic model and consider how this maybe applied to other polyelectrolyte-based systems as a general method for sub-micron patterning.

IKTS will present the synthesis and formulation of digital inkjet and aerosol jet printable material inks based on Ag, Au, Pt, Pd, Rh and Cu for the R2R printing of electronic components and sensor devices. The developed wet chemical precipitation method allows the synthesis of metal nanoparticles by a high yield. Based on these nanoparticles customized eco-friendly water based inks are formulated. These inks show a high compatibility with the printing process and a high shelf life. Critical ink and printing parameters are summarized and discussed. Due to the fact, that the industry uses a variety of electronic and sensory substrates, a method to adapt the curing temperature to low (polymer), middle (glass) and high temperature (ceramic) substrates for the printing of electronic conductors and sensor electrodes is presented. Important physical and chemical ink specifications like particle size, viscosity, surface tension, sedimentation stability as well as electronic conductivities and adhesion of printed films will be shown. Especially, solutions to optimize the adhesion, curing and electronic conductivity of printed films on low temperature substrates like PET are presented. Usually printing films are cured in conventional belt furnace. Here, we present a new millisecond functionalization technique, based on a line laser system. Thereby, the rapid curing of printed films on thermal sensitive substrates for R2R process is presented.

The roll-to-roll (R2R) coating processes with steel strip have developed for the high productive coating plants and therefore many steel mills have manufactured commercial zinc (Zn) coated steel products such as electro-galvanizing and hot-dip galvanized steel sheets by using R2R processes. Also, physical vapor deposition (PVD) processes like sputtering or e-beam evaporation can meet the demands of mass products with millions square meter of coated area and of very high quality level at the same time. However, the major problem associated with PVD process for Zn coating is a relatively low coating speed in comparison with conventional galvanizing line. Generally, commercial Zn coated steel products have to be produced with the moving speed over 100 meters per minute (m/min) and the coating thickness of a few micrometers. To overcome low coating rates, we focused to a new concept of coating process, which is called Electro Magnetic Levitation (EML)-PVD. As a result, we successfully fabricated EML-PVD system with a high deposition rate and a broad range of coating, and applied to the continuous R2R pilot line. Our wide EML-PVD pilot plant is consisted of four functional parts, including entry vacuum-lock, plasma pretreatment, EML coating, and exit vacuum-lock systems. In this report, the performance of a novel EML-PVD system will be presented. Also, Zn-magnesium (Zn-Mg) coatings were investigated by R2R EML-PVD process due to their excellent corrosion properties. The maximum dynamic coating rate of Zn-Mg coating showed approximately 70 μm-m/min. The uniformity of coating thickness within 1.2m wide steel strip was ±3%. As expected, The Zn-Mg coated steel sheets represented much higher corrosion properties than Zn coatings. Detailed properties and micro-structures of Zn-Mg coatings prepared by R2R EML-PVD process will be discussed.

The rational design and manufacturing of various surfaces to control droplet dynamics [1-3] is of significant importance in many industrial processes, especially those related to thermal management and microfluidic systems. However, the previous advances in droplet motion control at room temperature always become ineffective in the case of spray cooling, where the droplet transits to the so-called Leidenfrost state [4,5], due to the vigorous self-fluctuation, thermal marangoni forces and spray-induced aerodynamic drift. Through the modification of structural topography gradient and the imposed temperature, here we show that two simultaneous thermal states (Leidenfrost and contact boiling) can be manifested in a single droplet, thus engendering a preferential motion and subsequent confinement of droplet in the region with high heat transfer coefficient. The directional motion of water droplet and confinement of droplet can be maintained by extending the substrate to a structure with two-dimensional gradient. The further experiment elucidates that the droplet can be localized to any pre-determined location or exhibit different shapes under proper temperature range. We hope that our basic understanding of such Janus droplet can enable the rational design of high temperature thermal systems such as spray cooling and fuel injection.
Reference:[1] Chaudhury, M. K.& Whitesides, G. M. Science 256, 1539-1541 (1992).[2] Chu, K. H., Xiao, R.& Wang, E. N. Nat. Mater. 9, 413-417 (2010).[3] Liu, C., Ju, J., Ma, J., Zheng, Y.& Jiang, L. Adv. Mater. 26, 6086-6091 (2014).[4] Quéré, D. Annu. Rev. Fluid Mech. 45, 197-215 (2013).[5] Vakarelski, I. U., Patankar, N. A., Marston, J. O., Chan, D. Y.& Thoroddsen, S. T. Nature 489, 274-277 (2012).

The directional droplet self-propulsion on a solid surface [1-4] has attracted a lot of attention over the past few decades due to its potential applications related to analytical chemistry and bioassay. The previous studies have achieved extensive advances in controlling droplet self-propulsion dynamics by chemical heterogeneity or gradients of structural pattern. However, chemical gradient surfaces [5] may deteriorate due to migration or degradation of organic molecules in the long-term operation. In addition, the structural topography gradient that provides droplet with enough unbalanced interfacial energy for self-propulsion also renders itself with large contact line pinning force as droplet spreads, which can confine the droplet motion. To achieve a long-range droplet transport, here we propose a gradient surface with high-contrast wettability through the creation of two-tier roughness. Specifically, the intrinsically superhydrophilic region ensures a large wetting gradient over 100^o for droplet shifting, while the nanograssed superhydrophobic region greatly reduces the drag force associated with transport process. We further investigate the enlargement of droplet displacement compared to the surface with one-tier roughness, and relative dynamic model is developed to elucidate the enhanced driving force as well as the impaired pinning force. We hope that our design of gradient surface with large-contrast wettability can provide new perspectives for the better control of droplet dynamics.
Reference:
[1] Chaudhury, M. K.& Whitesides, G. M. Science 256, 1539-1541 (1992).[2] Ichimura, K., Oh, S. K.& Nakagawa, M. Science 288, 1624-1626 (2000).[3] Chu, K. H., Xiao, R.& Wang, E. N. Nat. Mater. 9, 413-417 (2010).[4] Cira, N. J., Benusiglio, A.& Prakash, M. Nature 519, 446-450 (2015).[5] Dos Santos, F. D., & Ondarcuhu, T. Phys. Rev. Lett. 75(16), 2972(1995).

An intriguing development of thin film transistor fabrication is employing single solution deposition of immiscible polymer blends to create layered structures. Polymer blends exhibit increased performance as thin film transistors relative to transistors made of a single polymer alone. These systems, consisting of mixtures of conductive and dielectric polymers, have shown a propensity to self-stratify during deposition, which can improve performance. Simply modifying deposition conditions can alter the morphologies formed by self-stratification of polymer blends. However, current use of self-stratification utilizes polymer blends specific for optimizing properties of the desired application, where the preferred deposition conditions are often identified by trial and error. This protocol does not provide insight into the governing factors in the self-stratification process.
A more thorough understanding of the role of kinetic and thermodynamic effects on the final polymer depth profile formed by self-stratification is required to offer crucial fundamental information that can be used to rationally improve the properties of thin film transistors as well as the ability to utilize self-stratification in the fabrication of a wide array of other systems and applications. Spin casting polymer blends is a non-equilibrium process, where increasing the speed at which thin films are cast decreases the film formation time. Our current research investigates the effect of spin speed on the self-stratification of a dielectric and conductive polymer blend in order to investigate the impact of the kinetics of film formation on the self-stratification process. We probe this effect by combining three themes: understanding solution phase behavior, monitoring film formation in-situ, and determining the depth profiles of the final film. Primary studies include blends of Poly(3-hexylthiophene-2,5-diyl) (P3HT), and Poly(methyl methacrylate) (PMMA). Initial results reveal that at short film formation times, P3HT is attracted towards the air interface. While when the spinning speed is decreased, and film formation time increases, the surface is saturated with P3HT, during which a P3HT rich layer is also formed at the silicon substrate surface. Although this groundwork surveys stratification for applications in thin film transistors, this research has potential to impact a wide range of technologies by developing a cost efficient method for multi-layer film deposition.

Indium Tin Oxide (ITO) is a widely used transparent conducting oxide (TCO). TCO films have been deposited by solution deposition process using ITO nanoparticle. However, it is difficult to obtain high quality ITO film at less than 200^oC because of high contact resistivity. The electrical properties of nanoparticle TCO films deposited by solution process should be strongly affected by the residual surface acting agent. Therefore, in order to obtain the high-quality nanoparticle TCO films by solution process with low resistivity, the after annealing temperature should be higher than 300^oC. In this study, ITO films were deposited on substrates by nanoparticle mist deposition(NMD) system . The deposition rate was almost equal to the one deposited by conventional sputtering depositions. The mist disposition process using a nanoparticle should be one of the most possible techniques for Roll-to-Roll process, because these ITO films were consisted by high crystalline crystal grain at low temperature.
ITO nanoparticles were dispersed in H₂O solution with surface acting agent by ultrasonic dispersion (20kHz). H₂O solution which include the ITO nanoparticle was atomized by ultrasonic transducer (2.4MHz).The solution mist were transported to substrate by carrier gas such as Ar or N₂. The sheet resistivity was around 100 ohm/sq, where the post annealing temperature was 200^oC. All the films showed more than 80% transmittance in the visible region. The transmittance decreased in the near-infrared region where reflectance increased. This behavior can be explained in terms of the variation in plasma oscillation in the near-infrared region, which is well known in highly degenerate TCO films. The capacitive touch-sensing device was fabricated by these Nanoparticle ITO. Lozenge-patterned ITO films were created by FPD Lithography Systems.

Polymer nanocomposite (PNC) materials have been a prominent scientific and industrial research area because of their demonstrated diverse functional properties and applications. A continuing challenge is to fabricate deliberately designed microstructures to optimize the overall performance of the hybrid materials. Herein, we introduce two facile methods towards realizing tunable NP structures involving a dispersion of polymer-grafted nanoparticles in a homopolymer matrix. In one method, the application of zone-annealing with soft-shear creates unidirectionally aligned highly anisotropic nanoparticle arrays in a chemically dissimilar homopolymer matrix with tunable aspect ratio. In another method, we demonstrate soft confinement patterning can generate high-density nanoparticle domains with well-controlled size, shape and location in both chemically identical and dissimilar homopolymer matrices. Both methods are applicable to versatile nanoparticle-polymer combinations and adaptable for roll-to-roll production.

NiZn-ferrite films were successfully prepared by inkjet printing technique. A theoretical model was employed to predict the optimal pitch condition for the uniform inkjet-printing of NiZn-ferrite films. The inkjet-printed NiZn-ferrite films were annealed at various temperatures from 700-1000 ^oC. The sintered NiZn-ferrite films were detached from the substrates and embedded into flexible polymeric films. Structural and Magnetic properties of the embedded NiZn-ferrite films were investigated by various characterization techniques such as X-ray diffraction, Field-emission SEM, vibrating sample magnetometer (VSM), and impedance analyzer. Bending test was also implemented in order to confirm if there is any degradation in the properties due to the embedment of the NiZn-ferrite films into a plastic film. Inductor coil was also printed by the inkjet on top of the sintered ferrite films for the demonstration of wireless power transmission. The coil-on-ferrite multilayer was embedded into a plastic film and used to receive magnetic field emitted from a power transmitting unit. Wireless power transmission was successfully demonstrated by turning on a LED light with the flexible embedded coil-on-ferrite films.

Technology is evolving towards thin, light, cheap and highly flexible smart electronic devices. Paper-based electronics are one of the most intriguing components of smart electronics due to their flexibility, easy processability and large scale production. Charge storage devices such as supercapacitors are included in this trend and can be easily integrated to paper based electronics. In this work, we simply brush painted graphene onto printing paper and then deposited polypyrrole (PPy) to fabricate hierarchical and hybrid supercapacitors. Electrochemical properties such as specific capacitance and cycling ability of the nanocomposite supercapacitors were then examined through cyclic voltammetry, chronopotentiometry, electrochemical impedance spectroscopy by three-electrode system and then compared to that of control samples with bare graphene and PPy. Fabricated supercapacitor electrodes showed encouraging results with a specific capacitance of 60 F g^-1 and good capacity retention with 85 % degradation upon 3000 cycles. Our method is cost effective, environmentally benign and can be easily adapted to roll-to-roll manufacturing.

Multilayer inkjet printing presents a promising method for fabricating bioelectronic devices with diverse functional materials over large area. [1, 2] A major motivation behind multilayer printing is the potential to construct 3D devices with new emerging materials, which are either difficult or impossible to implement using traditional microfabrication technology. Here we present a scalable and straightforward fabrication method using gold, carbon, polystyrene and polyimide inks for large-area printing of 3D electrochemical redox cycling sensors. Redox cycling is a sensitive electrochemical technique for detection of redox-active molecules. It is based on two electrodes that are independently biased at reducing and oxidizing potentials, respectively. [3, 4] The redox molecules undergo repetitive oxidation and reduction events by diffusing between these two electrodes leading to a large signal amplification.

In this work, we demonstrate the fabrication of redox cycling sensors by printing a gold nanoparticle ink for the bottom electrode and a carbon nanoparticle ink for the top electrode. The two electrodes are separated by a dielectric layer of polystyrene nanospheres. For the first time, we introduce polystyrene nanospheres as a novel nanoporous layer for separating two conductive electrodes. Furthermore, the distance between the top and the bottom electrodes is controlled by the thickness of printed nanoporous layer. In general, this distance plays a critical role for the redox cycling efficiency as there is a reciprocal relation between the signal amplification and the distance between the two electrodes.

We demonstrate the successful integration of the fabricated device for sensing ferrocene dimethanol as a redox-active probe. To enable redox cycling, we bias the top and bottom electrodes to an oxidizing and reducing potential, respectively. The sensor shows an enhancement in the overall Faradic current, which is 30 times higher in redox cycling mode compared to non-redox cycling mode, i.e., only a single electrode is used for electrochemical detection. Finally, we demonstrate the stability of the 3D printed sensors by cyclability test during electrochemical measurements.

References
[1] J. Jiang, B. Bao, M. Li, J. Sun, C. Zhang, Y. Li, F. Li, X. Yao, Y. Song, Adv. Mater. 2016, 28, 1420.
[2] B. K. Tehrani, B. S. Cook, M. M. Tentzeris, in 2015 IEEE Int. Symp. Antennas Propag. Usn. Natl. Radio Sci. Meet. 2015, pp. 607–608.
[3] D. G. Sanderson, L. B. Anderson, Anal. Chem. 1985, 57, 2388.
[4] M. Hüske, R. Stockmann, A. Offenhäusser, B. Wolfrum, Nanoscale. 2014, 6, 589.

Alkali-free thin glass exhibits high dielectric breakdown strength (11-14 MV/cm), volumetric energy density (38 J/Cm³) and excellent high temperature performance. Hence, it is a potential candidate for high temperature power electronic application. However, in order to improve reliability as well as manufacture wound capacitors, it is important to improve mechanical stability along with self-clearing phenomenon in glass. Polymer coating on glass is one of the possible methods to improve both these desirable properties. In this research work, polyurethane was successfully deposited on the glass by using dip-coating approach. We showed that the bending strength of glass was almost doubled while the bending radius was decreased by 2 times when 0.1 – 1 µm thick polymer was deposited on glass. The polymer coatings can heal existing defects on the surface and edge of the glass thereby improving the mechanical properties. We also found that ultrathin polymeric coatings did not alter the dielectric properties such as permittivity and loss of the glass. Development of coating methodologies can have a profound impact on next generation high temperature dielectrics for power electronic applications.

Silver nanowires synthesized by polyol route have high crystallinity and high aspect ratio. When those nanowires are deposited onto glass substrates over their percolation threshold, they can form transparent and conductive networks. These silver nanowire based transparent conductors show comparable transparency and sheet resistance values to those of commercial standard indium tin oxide (ITO) thin films [1]. As a result, this promising transparent conductor is used in various optoelectronic devices, such as solar cells, organic light emitting diodes (OLEDs) and photodetectors. The major challenge for silver nanowire electrodes is their stability against oxidation. So far, various organic and inorganic materials were studied as protective layer on silver nanowire networks. In this study, p-type nickel oxide (NiO) thin film is deposited onto silver nanowire networks via sol-gel method. All solution-based simple routes are used both for the synthesis of silver nanowires [2] and fabrication of the nanocomposite electrodes, which are capable for large area deposition. Depending on the nickel oxide thickness and the post annealing temperature, stability and the optoelectronic properties of silver nanowires are investigated. NiO thin films over 100 nm showed effective protection on silver nanowire networks with limited impact on transparency.

[1] S. Coskun et al. Nanotechnology 24 (2013) 125202.
[2] S. Coskun et al. Cryst. Growth Des. 11 (2011) 4963.

Large-area, low-cost fabrication of photonic crystals and metamaterials remains an outstanding challenge in materials and processing. Engineering refractive index at the mesoscale across large areas using conventional lithography techniques is costly and subject to considerable limitations in terms of defect sensitivity and compatible material selection. Soft lithography offers a low-cost, defect-tolerant technique for patterning layer-by-layer mesoscale structures across large areas. From a device standpoint, the need for flexibility of design iterations provides a niche for a low-capital-cost benchtop rapid prototyping system. A simple benchtop blade-coating apparatus is demonstrated to provide controlled inking of elastomeric stamps for residual-layer-free transfer molding of mesoscale patterns. Unstable and stable coating regimes are strongly dependent upon the stamp feature dimensions and ink properties.

Recently, organic semiconductors blended with polymeric binders have been the topic of intensive investigations as a promising approach to formulate organic semiconductor ink. In particular, the vertically segregated bilayer structures are fascinating considering that separate functional layers of the semiconductor and the gate-dielectric or semiconductor and the top-passivation layer in the OFET device can be deposited in a one-step film deposition process. In this presentation, we will introduce the first demonstration for centro-apical self-organization of organic semiconductors in a line-printed organic semiconductor:polymer blend. Key feature of this work is that organic semiconductor molecules were vertically segregated on top of the polymer phase and simultaneously crystallized at the center of the printed line pattern after solvent evaporation without an additive process. This unique printed structure was successfully demonstrated to produce the semiconductor and dielectric layers for the OFETs at one-step go printing. Furthermore, highly sensitive pressure sensors were demonstrated by using this double-dome microstructure originated from centro-apical self-organized of printed organic semiconductor.

A plasma-enhanced chemical vapor deposition (PECVD) is one of most commonly-used methods to grow various types of films and nanomaterials at relatively low temperatures in many research and industrial fields. However, in general, plasma enhanced reactions are huge complicated and hard to understand and control. Recently, we have proposed a new deposition method, so-called a radical-injection (RI)-PECVD system. This system has two-types of plasma sources stacked. One is a surface wave plasma (SWP) chamber at the upper side and the other is a capacitively-coupled plasma (CCP) chamber at the lower side. This enables us to control independently generations of H radicals by the SWP and carbon related radicals by the CCP. Furthermore, we have also established controlled synthesis of carbon nanomaterials, especially carbon nanowalls [1]. On the other hand, since amorphous carbon (a-C) films show a huge variety of optical and electronic properties, such as transparency, conductivity, and so forth, their application to various types of electrical and optical devices are strongly expected. However, such the device applications of a-C films are less advanced, because their growth mechanism and control technique of electronic properties are also not clarified and established yet. In this study, we synthesized a-C films by the RI-PECVD system, and investigated effects of radicals on growth characteristics and properties of a-C films with analyzing radicals by actinometry method and quadrupole mass spectrometer (QMS).
H₂ and CH₄ gasses were introduced into the SWP and CCP chambers, respectively. A 100 MHz VHF power (CCP power) was applied to the upper CCP electrode to control dissociation of CH₄ and related precursors. A total gas flow was varied from 50 to 400 sccm, in order to change gas residence time. The chemical bonding structure was analyzed by a near edge X-ray absorption fine structure (NEXAFS) spectroscopy.
With increasing the residence time, the sp²-C fraction once decreased and appeared the minimum value at 6 ms, then it increased again. At the residence time less than 6 ms, the peak widths of p* C=C and s* C-C peaks broadened at the shorter residence time, which means increase in fluctuation of bonding structures. In contrast, at the residence time more than 6 ms, the increase of sp²-C fraction can be interpreted that film deposition occurs dominantly with the species such sp²- and sp-hybridized hydrocarbons. The variety of radical species affect the bonding configuration in the a-C films via unresolved complex reactions both in gas-phase and on surface. Optical emission spectra showed that the relative intensity of the CH emission increased with decreasing residence time. We will discuss gas-phase and surface reactions based on detailed results by actinometry method and QMS in our presentation.
[1] M. Hiramatsu, K. Shiji, H. Amano, and M. Hori, Appl. Phys. Lett., Vol. 84, No.23, pp. 4708-4710 (2004)

reduced Ag nanoparticles
We developed a method for deformation-assisted direct imprinting of thermally reduced Ag nanoparticles to fabricate high-performance metal grid transparent conductors (TCs). In an reservoir-attached mold, a microscale grid-patterned cavity was connected to m acroscale cavity, so called “reservoir”, which led to improve ink filling inside the grid-patterned cavity by deformation-driven ink injecting from the reservoir. Also, the reservoir had a large cavity volume, which contributed to achieving minimum residual layers within the grid spacings due to thinner liquid film. The Ag nanoparticle structures fabricated using the typical mold and the reservoir-attached mold had the same linewidth of 4.1 μm, but the different heights of 2.1 μm and 800 nm, respectively. As a reservoir volume increased, the sheet resistance of metal grid TCs dropped steeply and the transmittance was increased. The metal grid TCs fabricated using the reservoir-attached mold performed better than the metal grids obtained using the typical mold in terms of the sheet resistance (5.0 vs 13.1 Ω/sq) and transmittance at 550 nm (92 vs 90 %), respectively. The metal grid TCs were embedded into a large-scale, flexible, and transparent polymer films, which showed a reasonable electromechanical stability under repeated bending. The metal grid embedded TCs were applied to touch screen panels.

It is generally believed that particles delivered by inkjet printing must be substantially smaller than the nozzle diameter of the droplet generator. Hence most reports on the inkjet printing of 2D materials such as graphene have used inks containing flake suspensions with mean diameter < 1 μm. Here we demonstrate that it is possible to inkjet print inks containing graphene oxide (GO) flakes with mean diameter > 50% of the nozzle diameter and that individual flakes considerably larger than the nozzle diameter can be printed with no significant blockage of the printer or damage to the flakes. Stroboscopic imaging shows the drop formation process to be identical to that observed with conventional inks. Polarised light images indicate that prior to drop formation there is alignment of the graphene oxide flakes as the ink flows through the droplet generator and this,combined with the flexibility of the 2D materials in the ink allows the curving or folding of the sheets to fit within a droplet.

After printing, the flakes show no greater level of folds or defects than found in the original flakes prior to the process. The bulk electrical conductivity of these ultra-large flake printed films is 2.48 × 10⁴ Sm^-1 after reduction to reduced graphene oxide (RGO), comparable with that reported with printed pristine graphene. The electrical conductivity of these printed films is only weakly dependent on the original mean GO flake size and coffee ring formation is suppressed when the flake size exceeds a critical value. These results indicate that the extreme flexibility of 2D materials allows very large flakes to be readily deposited by inkjet printing, hence enabling their use in large area deposition applications such as displays and flexible electronics.

Many electronic devices in current markets have special functional surface layer that has preventing scratches. Those anti-scratches layers have high hardness and are prepared with the conventional coating processes, dry processes and other deposition processes. Such rigid materials, susceptible to bending stress, and were those easily brittle fracture. However, in order to use such flexible display in recent years, the materials excellent in a flexible and scratch resistance have been sought.
Some of the companies have been developed a superior coating material to scratch resistance. And they are selling in markets. It can leverage a shape memory polymer, thereby realizing scratch resistance. However, they have insufficient self-healing at room temperature, auxiliary processing such as warming the healing process was required.
The authors, using a urethane is a material excellent in durability, we developed a surface coating material having a function to repair the like dent by abrasion and marketed. In particular, to achieve self-healing at room temperature obtained in practicality, and have developed excellent in durability.
In this presentation, we report on the urethane materials design and development of the polymer, and lubricity, slip resistance and durability to give additives those were carried out in order to achieve the self-healing function. The Tc (crystallization temperature) of those polymers are optimized by controlling the structure of the polymer molecule chains. In addition, to optimize the amounts of lubricants, slipping agents, and others were designed as industrial materials. The coating materials are blended with anti-aging agents in order to improve the durability.
Self-healing coating materials were realized by these blends materials are those satisfying self-healing function and durability required by the electronic devices industry. It is applicable to the current flexible display development progresses.

There is currently a burgeoning interest to study novel ink formulations and additive manufacturing methods for the next generation of flexible devices for energy applications. Although the continuous – flow direct writing process has been introduced more than a decade ago, it has recently re-emerged as a promising enabler of exciting energy device prototypes such as micro-batteries and light emitting diodes. This is because of the significant advantages that it offers, compared to other printing methods. Such advantages include precise deposition of a wide variety of ink viscosities, increased design space for new ink formulations, ability to write in 2D and 3D over large areas and non-vacuum conditions, and utilization of non-planar substrate geometries.

In this work we report on the relations between synthesis, continuous - flow direct writing parameters, and low energy intensity post-processing of hybrid TiO₂ aqueous ink formulations. Such inks are printed on heat sensitive polymer substrates for dye solar cell photoelectrodes but their versatility spans a wide range of other applications from sensors to photocatalysts. For the ink formulation we use an initial crystalline nanoparticle TiO₂ phase that provides the main functionality of the printed films. We also add a Ti-precursor that, when post-treated, provides connecting paths for the initial phase thus forming continuous porous structures. We find that the ink’s formulation plays a pivotal role by providing the means for tuning its rheological properties, the ink-substrate interactions, and the printed microstructures. We further discuss the implications of such compositional variations, introduced when adding polymeric agents such as polyacrylic acid or polyvinyl pyrrolidone, on the crystallization of the Ti-organic precursor into TiO₂ bridges. We finally report on the electrical properties of the printed TiO₂ photoelectrodes as compared to conventionally fabricated counterparts. The design, continuous – flow direct writing, and the subsequent mild thermal-energy treatments of hybrid sol-gel based TiO₂ inks may hold the key for large-scale and sustainable manufacturing of flexible dye solar cell photoelectrodes.

Ion gels, consisting of ionic liquids and structure-forming polymers have attracted attention as a gate dielectric layer because of their excellent properties such as thermal and electrochemical stabilities, negligible vapor pressure, and large ionic conductivity and capacitance. In order to generate ion gel layers on a desired surface of electronic devices, wide variety of simple solution processing methods including conventional solution casting, aerosol-jet printing, spin coating, and flexographic transfer printing have been demonstrated. However, alternative processing strategies are desirable to provide a diversity of process methods and to realize low cost, large area production of printed electronics. In this regard, a spray coating technique was applied to fabricate thin film transistors that operate at low voltages with high turn-on device currents. Transistor fabrication started from sequentially spray coating a regioregular poly(3-hexylthiophene) (P3HT), an ion gel gate dielectric, and gate electrode on pre-patterned source/drain contacts. All spray-coated transistors exhibited low operation voltages below 2 V, low turn on voltage at around 0 V, and reasonably high on/off current ratio above 10⁴. These results show that the spray printing technique provides a promising and reliable route to employ an ion gel layer and also to fabricate all printed thin-film transistors and other electrochemical electronic devices.

Inkjet printing of gold metallic contacts has been considered as an alternative to the more traditional pattern lithography techniques, as it is more efficient in terms of time and materials cost. For inkjet technology, most ink formulations for printing gold conductive patterns employ organic ligands as stabilizer and organic solvents as dispersant. This kind of formulation is not environment-friendly, especially in the use of organic solvents. Also for some printers, organic solvents are not compatible with it.

This study sought to address this issue by formulating gold inks using environment-friendly materials and using aqueous-based suspensions. Gold nanoparticles (AuNP) were synthesized from the Au³⁺ precursor solution using starch, a natural polymer, as both the reducing and stabilizing agents. The prepared AuNP inks were characterized using dynamic light scattering (DLS) and UV-Visible spectrophotometry. It was then inkjet printed on an etched fluorine-dope tin oxide (FTO)-glass substrate, and then sintered at 500 ^oC afterwards. Optical and electron microscopes were used to image the printed patterns, and the conductivity was measured using an electrochemical workstation.

To vary the size, concentration, and possibly the stability of the AuNP inks, the starch underwent partial acid hydrolysis prior to adding to the Au³⁺ solution. Different hydrolysis times were investigated and the average molecular weights of the hydrolyzed starch were determined using DLS. It was observed that longer starch hydrolysis time produced aggregated, and therefore unstable, AuNP ink. This is because longer hydrolysis time will expose the reducing ends of amylose and amylopectin in the starch. Basically, hydrolysis increases the amount of reducing agents in the starch solution.

During printing, the substrate was placed on a heating stage set at 80 ^oC to aid in the evaporation of the solvent upon contact of the drop on the substrate. After printing, the gold contacts were sintered to remove the starch and remaining water in the printed pattern. Thermogravimetric analysis (TGA) was also done to probe the process during sintering. Minimal mass loss was observed beyond 100 ^oC as the amount of starch attached to AuNP is also very minimal.

The number of printed layers was also varied. This would have an effect on the apparent conductivity of the printed gold electrode. As the number of layers were increased, the conductivity value slightly increases. However, with 30 or more layers, it started to delaminate easily from the substrate. Printing 10 layers for line patterns is sufficient enough to make it conducting.

Gold ink formulation using a natural polymer – starch – was studied for inkjet printing of electro-conductive patterns. This technique offers more environment-friendly approach to fabricating micro-devices requiring gold metal contacts.

Recent semiconductor process has been based on a vacuum system, which limits throughputs and cost. Printed electronics process is the process grafted by paper printing technology of large quantity production, so that it can reduce the cost up to 1/1000 without vacuum-incorporated process. Printed electronics is based on ink transfer process from one substrate to another. However, imperfect transfer of ink makes short circuit and the accuracy of pattern resulting in the degradation of device reliability. Transfer rate of ink can be improved when the difference of surface energies between two substrates is large, so that extra fine control of surface energy widens the range of ink choice which could not be achieved by previous fabrication technology of R2R equipment. Polymer-based roll and blanket are key components for recent printed electronics. They are very cheap and feasible for mass production. However, since their physical and chemical stability is poor, regular replacement of them should be needed. Also, fine control of surface energy is hard to be achieved by polymer-based materials, so that the combination of usable inks, roll, and blanket is confined within very narrow limits.
In this work, we developed atomic layer deposition (ALD) processes of ceramic rare earth oxides (REOs) and investigated their surface energies. Since ALD provides large area uniformity, excellent conformality, and precise thickness control at the atomic scale, ALD process is beneficial for conformal and uniform coating. We observed all ALD REOs of 50 nm have strong hydrophobic properties above 100°. In addition, surface energy of ALD REOs on Si substrate was changed from ~15 to 45 mN/m by changing film thicknesses from 0 to 50 nm. The surface energy of surfaces was minutely controlled since thickness of films was precisely controlled at the atomic scale. Although REO films show strong hydrophobicity, the nanoscale thickness is not enough to block the interactions between the surface and the substrate, so that the hydrophobicity of films was reduced resulting in surface energy control. This method is very unique for controlling surface energy, since there has been almost no investigations on both the developments of inorganic hydrophobic materials and accompanied nanoscale coating method. In addition, thermal stability of them was investigated at 500 °C annealing during 2 hours in air. Finally, we demonstrated various liquids transfer system by using surface-energy-controlled substrates of ALD REOs. The ALD REOs can make the fabrication of customized surface in R2R system, which is needed for the target applications using specific inks. Thus, it can be applied to use various kinds of inks which could not be used in R2R system before, and is expected to widen the applicable range of printed electronics for future semiconductor field.

As the use of electronic devices increases, electromagnetic shielding materials come into prominence. Although the 18 – 40 GHz frequency range has traditionally been used for military applications, recently some commercial telecommunication applications were started to used within the same frequencies. As a result, development of shielding materials which are effective above 18 GHz become crucial. In addition, it is also important to provide an efficient shielding material which is cost effective, scalable and light weight. Conductivity is one of the most important requirement for shielding materials and silver is known as one of the most conductive metals. Silver nanowires received much attention within the last few years due to their extraordinary properties inherited by bulk silver. Recently, silver nanowire based transparent conductors used in various optoelectronic devices such as light emitting diodes, solar cells and photodetectors [1]. In this work electromagnetic shielding efficiency of silver nanowire networks deposited onto polyethyleneterephthalate (PET) substrates were investigated. Processes, such as solution synthesis [2] and spray deposition, those are suitable for large-scale roll-to-roll manufacturing were used for the fabrication of the shields. Spray coating procedure enabled precise control on the silver nanowire density within the network and consecutively on the corresponding shielding characteristics. Fabricated Ag NWs/PET shields showed 40% absorption within 18-40 GHz range at an optical transmittance of % 83. Lifetime and flexibility characteristics of the shields were also monitored in conjunction with their shielding characteristics.

[1] S. Coskun et al. Nanotechnology 24 (2013) 125202
[2] S. Coskun et al. Cryst. Growth Des. 11 (2011) 4963.

We report a comprehensive study on the optical and electronic properties of hierarchical metal nanomesh (NM)/microgrid (MG) structures to determine their performance as transparent conductors (TCs). The NM helps deliver or collect carriers locally while the lower resistance MG transports carriers over larger distances. The structures exhibit high uniformity of optical and electronic properties. Hierarchical Ag NM/Ag MG structures demonstrate 83% diffusive transmission at a sheet resistance of 0.7 Ω per square when fabricated directly on quartz and 81% at 0.7 Ω per square when fabricated directly on flexible plastic. The direct current to optical conductivity ratios σ_{dc}/σ_{op} of these structures are 2900 and 2300, respectively. This corresponds to over an order of magnitude reduction in sheet resistance with a negligible to slight reduction in transmission compared to NMs. The haze factor of these structures may be tuned by modifying the NM hole diameter. Furthermore, the hierarchical structures exhibit good durability under bending and heating.

2D planar nanopatterns are of great interest in many fields as they can be utilized to a big array of applications from functional films to thin-film devices. However, typical methods to make 2D patterns based on laser interference and e-beam lithography along with some nonconventional approaches (e.g., self-assembled block copolymer-templated patterning) often suffer from low fabrication throughput, area limitation, and high cost.
To this end, we develop a simple but versatile methodology for scalable and high-throughput fabrication of 2D nanopatterns via sequential continuous 1D nanopatterning strokes enabled by Dynamic Nano-Inscribing (DNI) and Vibrational Indentation-driven Patterning (VIP) [1]. DNI inscribes and VIP indents 1D micro/nano-grating patterns in a continuous manner on flexible substrates with controlled period and depth. By combining these 1D patterning strokes in series, various 2D patterns of desired topology can be continuously ‘direct-written’. Further, by adopting a grating-containing DNI tool in VIP processing, a ‘single-stroke’ 2D patterning can also be realized [2].
Many applications can benefit from the presented 2D nanopatterning strategy, particularly requiring large area and high throughput. In particular, 2D-DNI realizes a well-defined ‘nanovoid’ pattern which can be capitalized in manifold applications such as electronics and bioengineering templates especially requiring good scalability and reproducibility. As an example, we present one specific use of such a nanovoid pattern: a size-selective docking of nanoparticles (NPs) in solution, demonstrated by a microfluidic cell experiment in conjunction with in-depth simulation analysis [3]. Fluorescently labeled, negatively charged polystyrene NPs of the diameter matching to the void size are effectively confined in the positively charged nanovoids. This demonstration may be just one example among what our 2D patterns can be used for, specifically targeting commercially-feasible scales.

* This work was supported by the National Research Foundation of Korea(NRF) Grant funded by the Korean Government(MSIP) (No. 2015R1A5A1037668).

References:
[1] J. G. Ok, S. H. Ahn, M. K. Kwak, and L. J. Guo, Continuous and high-throughput nanopatterning methodologies based on mechanical deformation, J. Mater. Chem. C, 1, 7681-7691 (2013).
[2] J. G. Ok, A. Panday, T. Lee, and L. J. Guo, Continuous fabrication of scalable 2-dimensional (2D) micro- and nanostructures by sequential 1D mechanical patterning processes, Nanoscale, 6, 14636-14642 (2014).
[3] L. Chen*, A. Panday*, J. G. Ok, and L. J. Guo (*equal contributions), Size-selective and spatial confinement of nanoparticles in sinusoidal nanovoid patterns by exploiting ionic entropy, submitted.

Inspired by the multifunctionality of biological surfaces necessary for the survival of an organism in its specific environment, we developed a special wetting polymeric nanofur surface which can be adapted to perform different functionalities necessary for efficient oil/water separation. Nanofur is fabricated using a highly scalable hot pulling technique, in which nano- and microhairs are drawn out of the softened polymer surface with a heated sandblasted steel plate. By using a set of simple modification techniques nanofur can be adapted to perform different types of oil/water separation: selective separation of water or oil, control of oil absorption capacity and continuous separation of oil/mixtures by filtration.
As-prepared nanofur is superhydrophobic and superoleophilic, and selectively absorbs oil from oil/water mixtures. By changing the nanofur fabrication parameters its oil absorption capacity can be controlled. Microperforation of the nanofur films results in a porous nanofur membrane capable of selective separation of oil from oil/water mixtures in a continuous gravity driven filtration process. Alternatively, the surface properties of the as-prepared material can be changed to underwater superoleophobic by plasma treatment, enabling the selective removal of water instead of oil from the oil/water mixtures by filtration. All of the presented techniques can be applied to a wide selection of polymeric materials, including biodegradable and recyclable polymers, thus, reducing the environmental impact of oil/water separation processes.

We report recent progress of printable thin-film and e-textile sensors for health-monitoring applications [1-2]. First. We describe printable thermal sensors based on composites of semicrystalline acrylate polymers and graphite. The sensors exhibit changes in resistivity by six orders of magnitude or more for a change in temperature of only 5 °C or less under physiological conditions with high repeatability (1,800 times). Device performance is practically unchanged by bending to radii below 700 µm. The devices exhibit a high sensitivity of 20 mK and a high-speed response time of less than 100 ms. Then, we report a printable elastic conductor with a high initial conductivity of 738 S/cm and a record high conductivity of 182 S/cm when stretched to 215% strain. The elastic conductor ink is comprised of Ag flakes, a fluorine rubber and a fluorine surfactant. By using printable elastic conductors, we demonstrate novel applications including a wearable electromyogram sensor printed onto a textile garment. This work is financially supported by JST/ERATO Bio-harmonized electronics project.
[1] T. Yokota, et al., PNAS 112, 14533 (2015).
[2] N. Matsuhisa, et al., Nature Communications 6, 7461 (2015).

Tattoo-based electronics has emerged as a powerful platform for interfacing technology with the human body. Several notable examples of active and passive devices able to adhere and conform to the human epidermal tissue have been hitherto proposed, the aim being the development of electronic skin sensors and actuators for motion and vital signs monitoring. Nonetheless, the tattoo-based simple and reliable transfer technique, along with a careful choice of the materials, may open organic electronics to a new range of systems and applications in the emerging world of edible devices. The functions targeted by edible electronics include biosensing and bioactuation from within the gastrointestinal tract, as well as food quality monitoring, and it would naturally benefit of low-cost, up-scalable material deposition techniques, such as inkjet printing.

In this work we demonstrate the fabrication of all-printed biocompatible p-type and n-type transistors on commercial temporary tattoo paper and their subsequent transfer and operation on different edible objects. The materials employed for the devices are either biocompatible, nature derived or commonly used in the food industry. PEDOT:PSS, a very well known biocompatible conducting polymer, constitutes the transistors’ contacts and gate electrode. Alternative conductive materials can be adopted, e.g. edible gold and silver. Shellac, a biodegradable bug secreted resin, acts as dielectric, while biocompatible polymer semiconductors are employed as active materials. The TFTs fabrication is followed by their deposition onto various edible objects by means of an easy and reliable transfer and release technique. Indeed, the tattoo paper consists of a submicrometric ethylcellulose layer attached to a paper sheet by means of a sacrificial water soluble starch layer, and the transfer occurs as in common temporary tattoos for children: the printed circuitry is pressed on the object of destination and wet with water to allow the release of the paper. Electrical measurements in inert atmosphere and in air after the transfer prove the robustness of the technique, and evidence of the stability in air of the devices is presented along with an example of complementary logic circuit.

The present work thus demonstrates the all-printed realization of both p-type and n-type biocompatible transistors, enabling robust complementary logic circuits, on a commercially available edible tattoo paper. The devices thus produced can be directly applied to different ingestible substrates such as food and pharmaceutical capsules, and therefore constitute an interesting approach towards the realization of edible circuitry for biomedical and food quality monitoring applications.

Bandodkar, A.J., et al. (2015). Electroanalysis 27.3, 562-572.
Fattahi, P., et al. (2014). Advanced Materials, 26(12), 1846-1885.
Irimia-Vladu, M., et al. (2013). Green Chemistry, 15(6), 1473-1476.
Bettinger, C.J. (2015). Trends in Biotechnology 33.10, 575-585.

Traditionally printed and flexible devices were mainly applied to displays and solar cells. In recent years wearable electronic gadgets and Internet of Things have also been identified as potential areas where added flexibility, conformability and lower fabrication cost are desired. The shift in applications may bring new opportunities for printing technologies as lifetime requirements for wearables is different than that of large area electronics. The focus of materials development however remains the same. Printable materials need to be stable in air and processing cannot compromise the electronic performance of materials. Most systems are composed of sensors, electronic circuits and power sources. We have focused our research efforts on printing light sources, photodetectors, batteries, solar cells and passive components. Using these devices as building blocks, we combine screen-printing, inkjet printing, spray deposition and blade coating to integrate devices and demonstrate systems. In this talk, we will discuss details of each printing process and the design of an energy storage and harvesting system for wearable electronics. The battery consists of printed anode and cathode layers based on graphite and lithium cobalt oxide, respectively, on thin flexible current collectors. It displays energy density of 6.98mWh/cm2 and demonstrates capacity retention of 90% at 3C discharge rate and ~99% under 100 charge/discharge cycles and 600 cycles of mechanical flexing. A solar module with appropriate voltage and dimensions is used to charge the battery under both full sun and indoor illumination conditions, and the addition of the solar module is shown to extend the battery lifetime between charging cycles while powering a load. Furthermore, we show that by selecting the appropriate load duty cycle, the average load current can be matched to the solar module current and the battery can be maintained at a constant state of charge. Finally, the battery is used to power a pulse oximeter, demonstrating its effectiveness as a power source for wearable medical devices.

In flexography, while elastomeric stamps with micrometer feature resolution can be manufactured, challenges to print micrometer-scale features arise in loading the stamps with a thin layer of ink and controlling the quantity of ink transferred to substrates. As a result, the limited resolution (~10-50 μm minimum feature size) of flexography prevents its widespread use in printing high-performance electronic devices. Recently, it has been shown that flexography using nanoporous stamps can overcome this limit, via nanoscale control of ink transfer within arrays of microstructured carbon nanotubes (CNTs) conformally coated with an ultra-thin low surface energy polymer by initiated chemical vapor deposition (iCVD). Using this method, direct printing of features with micron-scale lateral dimensions (<5 μm), fine-edge roughness (<1 μm) and highly uniform thickness in the sub-100 nm range has been demonstrated via simple mechanical contact with pressures of the order of a few kPa. Further understanding and optimization of this process is necessary to establish apriori control of the film thickness, and enable optimal design of nanoporous stamp materials.
In this work, we study the mechanism of ink transfer from nanoporous stamps to solid substrates, and elucidate how the uniformity and thickness of the printed ink depends on the geometry, porosity, and mechanics of the stamp. Experiments are performed using a custom-built setup in which microstructured stamps (1-100 μm lateral dimension) loaded with colloidal silver ink are brought into contact with a plano-convex glass substrate. A flexure-based compression system allows precise control of the printing force (resolution ~1 mN) and time (resolution ~1 msec), and the interface between the stamp and the substrate is imaged in real-time. Using this approach, we quantify the relationship between force, transfer ratio, and printed layer thickness, owing to the curved-flat lens geometry that allows us to calculate the contact pressure distribution across the printed area. We find that the transfer ratio depends on pressure but the pressure does not appear to influence the printed ink thickness. Based on these findings, we consider a model of the stamp-substrate interface as an array of parallel nanotips with normally distributed height variation, wherein accumulating contact of the ink-loaded tips occurs as the pressure is increased. We use this approach to estimate how the thickness of the liquid layer scales with stamp porosity, nanotube radius, and height variation; and further we consider how elastocapillarity influences withdrawal of the stamp from the substrate.

The need for less crowded frequencies and higher bandwidth has driven the development of millimeter wave communications devices (>30 GHz). These devices are also inherently smaller, providing an advantage for low size, weight and power (SWaP) systems. High resolution 3D printing would be a useful tool for the rapid development of this class of device, but there is a lack of printable dielectric materials specifically designed for use in this frequency range. Such dielectric materials require low loss in that frequency range, something only possible for materials with low dipole moments. Presented here are printable high-K dielectric polymer-inorganic hybrid materials designed for high frequency RF applications. By varying materials composition, the dielectric constant of printed features can be tuned from 2.2 to over 20.

The ability to print a wide range of 3D architectures using these hybrid materials is demonstrated, including those composed of solid, high aspect ratio (e.g., vertical walls), and spanning features. The dielectric properties and the loss tangent of solid blocks were measured and found to be comparable to best in class commercial materials. Several hybrid inks were used in the fabrication of simple band-pass filter devices. The device responses were measured in a waveguide across the K_a band and compared with predictions from finite element modeling. There is strong agreement between the predicted and observed transmission, with the transmission range changing with the dielectric constant of the material as expected.

In the field of nanoelectronic sensors, numerous concepts have been developed that exploit the bulk properties of carbon nanotubes (CNTs) in films and networks. However, a significant part of the often-quoted superior advantages of CNT devices, such as ultra-small footprint and potential for highest sensitivity and specifity, require a proper correlation to the intrinsic properties of CNT materials. This condition is fulfilled only by an individualization and/or a nanoscale alignment of single or small-bundled CNTs. Additionally, the development of sufficiently mild concepts for CNT sidewall functionalization for debundling and grafting which do not alter the electronic band structure of the CNTs is a challenge. In recent years, significant progress has been made to obtain nanoelectronic devices such as CNT field-effect transistors (CNT-FETs) with significant performance figures and device uniformities suitable for micro-nano sensor applications. This contribution presents recent achievements to fabricate arrays of nanoelectronic field-effect transistors on silicon wafers (diameter 200 mm) as a sensor element, using individualized and aligned semiconducting single-walled CNTs as the active channel material. Dielectrophoretic deposition of CNTs from liquid dispersions turns out to be a scalable solution for the integration of one-dimensional nanomaterials into microelectronic electrode structures achieving CNT-FETs with relevant performance figures (drain currents >100 nA, on-off ratios >100). Attempts to develop these CNT-FET devices to optical sensors will be outlined, investigating the individual roles of intrinsic CNT light absorption, light-sensitive Schottky barriers at the CNT-metal contact interface, and effects due to a decoration of the CNTs with plasmonic nanoparticles [1]. We further highlight that such a decoration of solids from a chiral mixture of semiconducting single-walled CNTs reveals bundles with a segregation of CNT diameters along the radius of the bundle. A careful Raman spectroscopy analysis of CNTs decorated with metal nanoparticles shows that the radial breathing modes of higher wavenumber are selectively affected. This observation indicates a preferential ordering of the CNTs with smaller diameter at the bundle periphery [2].

Printed batteries are an emerging energy storage technology, providing on-device power sources for wireless and flexible electronics applications. While partially printed battery systems have been demonstrated, fully printed batteries would enable seamless additive manufacturing of integrated systems such as wearable electronics or printed radio-frequency identification (RFID) tags. Silver-oxide batteries are well suited for these applications based on their high energy density and air stability but have not been designed to meet the processing requirements of a fully printed battery with a vertical geometry. For this system, electrodes and current collectors must be chemically compatible with the electrolyte environment, printed at low temperatures to avoid electrolyte dehydration, and achieve high conductivity to prevent series resistance losses in the battery. Traditionally, silver current collectors are used in printed batteries, but these significantly add to the cost of the stack and corrode over time in the electrolyte environment. This work addresses these challenges by developing printed carbon separators and current collectors for fabrication of fully printed silver-oxide batteries. The resistivity and porosity of stencil-printed carbon films were investigated as a function of printing temperature and stencil thickness to determine optimal printing conditions. Printed silver-oxide batteries were prepared with carbon separators and current collectors printed directly in the battery stack. High areal capacities of 6-8 mAh cm^-2 were achieved with C/2 to 2C discharge rates, exceeding the performance of previously reported printed batteries. Self-discharge lifetimes of one month were obtained with the use of a PDMS encapsulation layer. Internal resistance of these cells was comparable to printed batteries in the literature (≤ 30 Ω) with active electrode utilization of at least 70%. This work represents the first demonstration of printed carbon separators and current collectors, a step towards realizing low cost, fully printed batteries that do not require the assembly of individual layers.

Printing electronics has been viewed by many as an exciting proposition to mass produce large area electronic devices such as displays or imaging arrays. This original promise has only partly materialized, however, today we see an even more exciting opportunity to turn printing into a manufacturing technique for complex systems comprising sensors, communication, power and other components, including not only functional materials but also microchips. This talk will describe our journey to uncover these opportunities from printed transistors to hybrid integrated systems for smart labels and wearables. Printing will be presented as a technology that is poised to revolutionize electronics manufacturing enabling new form factors, complex shapes and tighter integration of functionality with everyday objects. Special attention will be given to new results on microassembly of chiplets for heterogeneous integration of logic, MEMS, sensor and analog components. These approaches will ultimately lead to new levels of integration and enable on-demand electronics devices for customized IOT applications.

Active inkjet materials are invoked in the fabrication of optoelectronic devices. These types of multilayer assemblies contain a variety of commercially available ink formulations. It is envisioned that a dielectric SU-8 material can be used in a FET or PN junction-like structure to form an interlayer between conductive silver and semi-conductive MWCNT-doped PEDOT:PSS ink layers. These printed structures may be fabricated onto a porous TiO2 transport material lying on a glass substrate or a polyimide based flexible substrate, for instance.These structures are a starting point for offering valuable information on layer-on-layer printing interactions and interface problematics within a complete inkjet device fabrication.
A major portion of this work is dedicated to optimizing printing parameters. Parameters such as the spacing between each drop, the drop volume, the ink temperature as well as the chuck temperature are key in printing homogeneous layers. This is important for obtaining the desired electrical and mechanical properties of the ink layers. In layer-on-layer printing, the optimization process of the printing parameters is essential to control the inter-layer adhesion properties since the printed ink layers act as the printing platform for the next layer. This optimization process is performed for each ink and combination of layers used in the fabrication of these structures. Methods of optical post-printing treatments are also investigated and used in the sintering/curing process of the thin ink layers to avoid mixing of the different materials at the interfaces. Local laser post-processing techniques are preferred since this allows for the use of low-temperature flexible substrates, which are currently not possible when using conventional furnace thermal treatments. In previous work, the INO MOPAW laser platform was demonstrated to offer a unique pulse shaping ability in order to produce very efficient sintering/curing processes. In addition, finite element method simulations of laser post-processing on thin printed metallic ink layers support our findings in the identification of the optimal laser sintering parameters. Finally, electrical and mechanical characterization has been performed on the printed layers to assess the process development from the printing to the post-processing steps. The validation of the interface quality between the different layers and on the desired overall microstructures properties will also be presented.

Sensors are widely used in many different fields, from safety related applications, to healthcare and biomedical related applications. Therefore, new and improved sensor systems are made possible both with new materials and processing technologies.
This talk summarizes the developments in laser based direct writing techniques of carbon based materials for applications as active materials in miniaturized chemiresistor sensors.
Carbon materials such as carbon nanotubes (CNT) and hybrid CNT, i.e. decorated with nanoparticles, are very promising sensor materials, with high sensitivity and fast response times. In this talk, laser direct writing of CNT and hybrid CNT onto nonconventional substrates, i.e. flexible materials, etc. for the fabrication of sensors is presented. The direct writing technique is based on laser-induced forward transfer (LIFT), a simple process where a laser beam is focused through a transparent substrate onto a material film to be transferred. Every laser pulse results in the transfer of the active material onto a substrate that is usually placed parallel and facing the thin film at very short distances.
With LIFT, CNT and hybrid CNT materials are transferred, with a transfer yield of nearly 100%, to fabricate chemiresistive devices. The as printed carbon material maintains its original geometry, and the chemical and structural properties with high fidelity.
In addition, the performance of the LIFT-ed sensors, i.e. the sensitivity, and response time was evaluated at room temperature, by exposure of the sensors to different toxic vapors. Different sensitivities to the selected analytes i.e. acetone, ethanol, ammonia, etc. have been measured thus proving the feasibility of LIFT for applications in new and improved sensing devices.
Acknowledgements
This work was supported by a grant from the Commission for Technology and Innovation CTI (project no. 16713.1 PFNM-NM).

Rapid preparation of large-area hierarchical nanoporous films on flexible substrates will not only enhance the fabrication of light-weight and portable devices, but also reduce the fabrication cost by employing large-scale manufacturing methods, such as roll-to-roll processing. However, conventional synthetic methods to form porous structures usually require furnace calcinations of the materials at high temperatures of more than 500 ^oC for several hours, which is incompatible with polymer-based substrates. We report a simple strategy for the creation of large-area nanoporous silica or carbon-based hybrid films on polyethylene terephthalate via photothermal processing. This method enables the selective heating of light-absorbing thin films on low-temperature substrates using submillisecond light pulses generated by a xenon flash lamp. The film contains light absorbing species such as metal nanoparticles as the nano-heaters to convert light energy into heat, a sacrificial block copolymer surfactant to generate mesopores, and cross-linked polyhedral oligomeric silsesquioxane (POSS) or phenol resol to form the skeleton of the porous structure. Hierarchical porous structures are achieved in the films after photothermal treatment with uniform mesopores (41~48 nm) on the surface and interconnected macropores (>50 nm) underneath resulting from a foaming effect. One can choose the light absorbing species to impart function in the film subsequent to its fabrication. In one example to create functional films for sensors we demonstrate loading of gold nanoparticles at up to 43 wt % in the porous film with less than 2 wt % organic residue. This rapid and large-area synthetic process of porous structures is compatible with roll-to-roll manufacturing for the fabrication of flexible devices.

The development of effective modification strategies to improve the interface of the biological milieu with the electronics remains challenging. Especially in the case of electroactive cell recordings, it is essential to establish an ideal cell-to-cell as well as cell-to-surface communication network to improve the quality of the biological recordings. To this end, we demonstrate a direct and efficient approach for preferential cell adhesion and growth on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) surfaces. Specifically, selective laser ablation (Yb:KGW sub-ps laser at a wavelength of 343 nm) was used, to design either cell-adhesion (i.e., aminosilane, collagen etc.) or cell-repulsive regions (i.e., fluorinated silane) of various shapes, dimensions and aspect ratios onto PEDOT:PSS films. The high resolution user-defined micropatterns were constructed by ablating the functionalized layers on top of the electroactive surface. Studies using MDCK cells revealed preferential cell adhesion and growth following the pre-formed patterns, with significant precision. The proposed process provides a scalable and versatile strategy for the patterning of the electrode layers and the subsequent selective cell-growth towards high quality cellular recordings and high throughput drug testing.

Nanocrystalline metal oxides thin films with complex 3-D nanostructures achieving the large specific surface area are preferable for practical device applications with high efficiency and performance in energy and environmental fields. However, the large-scale manufacturing has been a significant challenge due to the requirements for low-cost industrialization: relatively simple setup, safe and pollution-free processing, low energy consumption, and high throughput production. Traditional physical and chemical vapor deposition processes, electrochemical methods, and wet chemical processes combined with post thermal annealing do not support low-cost and high throughput production of nanostructured crystalline metal oxides thin films, which would be supported by a potential approach through combing the rapid processing and high throughput production of industrial-scale pulsed light irradiation with the low-cost and scalable processing of metal-organic precursor solution deposition. Here we demonstrate a novel approach to the instantaneous photonic synthesis of 3-D nanostructured TiO₂ thin films through the pulsed photo-initiated decomposition accompanied by instantaneous self-assembly and crystallization processes achieved by pulsed light irradiating liquid photosensitive Ti-organic precursor films processed by spin coating. The instantaneous self-assembled 3-D nanostructure of the films consists of a dense bottom layer and a dendritic top layer, the latter can be simply controlled by changing either the precursor solution concentration or the spin coating cycles. Subsequent hundreds of pulses irradiation rapidly improved the crystalline quality of TiO₂ nanocrystalline films through pulsed photothermal effect. Under hundreds of pulses irradiation, the non-radiative recombination of photogenerated electrons and holes in TiO₂ nanograins, coupled with inefficient heat dissipation due to low thermal conductivity resulting from 10-30 nm nanograin size and thin structure, supplies enough heat to provide thermodynamic driving force for rapid improvement of the crystalline quality of nanocrystalline TiO₂ thin film. The resulting carbon materials from the photo-initiated decomposition are graphitic oxides coating TiO₂ nanograins and can be further reduced by the subsequent pulsed light irradiation. The oxygen plasma cleaning can completely remove carbon materials in the films. The demonstrated processing is applicable to instantaneous synthesis of other transition metal oxides films too. This novel approach opens a promising way of instantaneous photo-initiated synthesis combined with in-situ rapid photothermal treatment to the low-cost and high throughput production of nanostructured metal oxides such as TiO₂ nanocrystalline thin films for energy and environmental applications.

The wet chemical deposition methods such as ink-jet or screen printing using metal-based inks/pastes typically yield electrically insulating structures in as-printed state. The post-processing (functionalization) is required to remove the organic components, sinter the metallic particles, and enable electrical conduction in these structures. This is a critical technological step determining final morphology and properties of the printed materials. Presently, mainly the furnace-based methods, like muffle belt furnace and various types of rapid thermal annealing with typical processing times from 30 min to few seconds, are used. In case of printed metallic films, the standard approach often requires reducing atmosphere and, depending on material, processing temperatures above 800 °C. These conditions limit substantially the processing speed, narrow the range of applications and substrate materials, and increase the costs of the printed structures.
The present work focuses on the novel functionalization approach based on a micro-optically designed one dimensional diode laser source (diode laser arrays) having a line-shaped beam profile. The Ag, Au, Pt, and Cu films (thickness 1-2 µm) were ink-jet printed on different polymer, glass and Al₂O₃ ceramic substrates. The Ni and Mo films (thickness ~20 µm) were screen-printed on the ceramic substrates. All materials were processed in ambient air using diode laser arrays with dwell-time in the range of 100 µs - 30 ms and different laser power. The experiments show feasibility of reliable converting as-printed metal-based layers into highly conductive structures using this approach. In addition, it is suitable for selective processing of the printed Ag, Au, and Cu structures at the speed up to 60 m/min without damaging the thermally sensitive polymer substrates. This method enables single line-scan functionalization of the required area, i.e. selective sintering of the light absorbing structures on the full print layout width, in a R2R compatible manufacturing process, which does not require spatial or temporal laser beam scanning.
Even conductive Mo-based printed structures on ceramic substrates were realized by this method, which was impossible for the reference films annealed in oven in reducing atmosphere (850 °C, 6 min, 100% H₂). Achieving such properties by millisecond processing in air demonstrates the possibility of fast local heating of the printed structures to the temperatures well above 1600-1700 °C. This approach paves the way for fast functionalization of the printed refractory metal and even certain ceramic materials in the future.

Using the thermocapillary effect generated by the extreme thermal gradient from a focused laser beam, focused laser spike(FLaSk) dewetting has been shown as a promising method for nanopatterning of polymer thin films to develop micron and even sub-micron features with overlap effects. The lower viscosity and higher surface tension of metallic melts make the formation of extreme gradient dewetted features more complex on metal nanofilms, resulting in the formation of trench-ridge-dot structures in FLaSk dewetted line features on thin (20nm) gold films. In these structures, the gradient induced dewetting occurs simultaneously with the Rayleigh droplet forming at the edge of the heated region, where thermal gradient forces are relatively lower. When multiple line patterning is performed, by tuning the distance between two lines, moving rather than removing of material will result in sub-spot features. Shrinking the line distance coalesces droplets into ridge features, creating a trench-ridge structure at a sub-micron scale, which generates visible plasmonic effects. One implication of this phenomena is the ability to make ordered structures out of disordered stochastically dewetted droplets, which shows the power of laser dewetting to pattern film from a disordered state. To show this, highly-uniform trench-ridge structures were obtained from completely dewetted films with droplets of several sizes illustrating that metallic dewetting differs from almost every other form of lithographic patterning—obtaining highly uniform final structures does not require defect-free starting materials. That an ordered, continuous structure can be built, and furthermore erased on-demand from a disordered, discontinuous structure, opens the possibility for transient, programmable anisotropic conductivity and optical properties.

Recently there is a significant increase in studies of Laser Induced Periodic Surface Structuring (LIPSS) due to both practical and theoretical importance, in particular after the development of Nonlinear Laser Lithography (NLL) technique [1], which opens new areas for industrial applications of LIPSS, as an effective tool for controllable, highly-ordered large-area nanostructuring. In general, LIPSS patterns appear on the surface under the laser beam as periodical lines (ripples) with sub-wavelength periodicity, perpendicular or parallel to the laser polarization. The LIPSS patterns where the ripples form perpendicular and parallel to the laser polarization are known as “normal” and “anomalous”, respectively [2].
The commonly accepted physical mechanism for the creation of “normal” LIPSS is based on interference between incident laser beam and plasmon-polariton waves induced along the surface [3]. The creation mechanism of “anomalous” LIPSS is an interference of incident laser beam with dipole-like scattered waves along the surface [1]. Although many papers demonstrated creation of LIPSS on the same material (for example on Ti) where it is “normal” in one case [4], and “anomalous” in the other [1], there is no clear theoretical model explaining the switching mechanism between these experimentally observed patterns.
Here, we experimentally demonstrate a new approach for controlling the direction of the ripples by switching between “normal” and “anomalous” LIPSS. Guided by these experiments, we developed a theoretical model which successfully explains the switching mechanism between the two observed LIPSS modes. The mechanism relies on competition between two different feedbacks inherent in the LIPSS formation process: (i) a long range, low intensity dipole-like scattering of light, initiated by far-field dipole radiation, which governs “anomalous” ripples parallel to the laser polarization, and (ii) a short range, high intensity plasmon-polariton wave, initiated by near-field dipole radiation and responsible for creation LIPSS perpendicular to polarization, i.e., “normal” ripples. For the first time, we are able to create both types of LIPSS on the same surface by efficiently controlling these two feedback loops. Using NLL principles, highly-ordered, large-area nanostructured patterns are obtained in both “normal” and “anomalous” modes on different materials with a plethora of applications to diverse areas, including plasmonics, photovoltaics and micro/nano-electronics.

References:
[1] B. Öktem et al. Nature Photonics 7, 897 (2013)
[2] V. Emel’yanov et al. Soviet Journal of Quantum Electronics 14 no. 11, 1515 (1984)
[3] J. E. Sipe et al. Phys. Rev. B 27, 1141 (1983)
[4] J. Bonse et al. J. Laser Appl. 24, 042006 (2012)

Transparent n-type ZnO nanocrystals (NCs) have been synthesized by both liquid- and gas-phase methods and have composed electron transport layers (ETLs) in high-efficiency perovskite solar cells¹ and organic light-emitting diodes.² The highest electron mobilities, μ_e, (up to 3 cm²V^-1s^-1) have been achieved via nonthermal plasma synthesis integrated with aerosol deposition, which produces networks of intimately connected NCs with ligand-free surfaces.³ Attaining these high μ_e, however, has required high-temperature (340 ^oC) thermal annealing for at least one hour, which limits device incorporation and precludes roll-to-roll manufacturing.

We produce high-μ_e ZnO NC networks without thermal annealing by combining nonthermal plasma synthesis and supersonic impact deposition with xenon-flashlamp intense pulsed light (IPL) annealing. Previously, IPL has been used to increase the free electron density, n_e, of large-grain polycrystalline ZnO grown by chemical bath deposition,⁴ but a μ_e enhancement has not been demonstrated, and the effects of IPL on ZnO NCs have not been investigated. In our synthesis/deposition process, 9 nm NCs form from diethylzinc vapor and oxygen gas in a 6 Torr RF plasma, accelerate through a thin nozzle to supersonic velocity, and impinge on a variety of substrates at room temperature, forming porous (60% porosity) thin films at a deposition rate of 10 to 20 nm/s. The as-deposited NC surfaces are terminated in electron-trapping OH groups, which we remove by infilling the pores with Al₂O₃ by atomic layer deposition (ALD); an 8 nm Al₂O₃ coating yields air-stable films with n_e = 7 x 10¹⁸ cm^-3_. (For ETLs, n_e can be lowered by reducing the Al₂O₃ coating thickness.) Prior to ALD, we use 1 ms IPL flashes with a surface power density of 12 kW/cm² to selectively heat and sinter the ZnO NCs, which strongly absorb the UV portion of the incident radiation. Varying the number of flashes from one to one thousand, we gradually increase the NC-NC contact area and thereby tune μ_e from approximately 0.1 to 0.6 cm²V^-1s^-1. Then, applying additional flashes after ALD, we increase n_e by up to a factor of four and thus induce a transition from variable-range hopping to metallic conduction, attaining μ_e as high as 1.5 cm²V^-1s^-1. The mechanism of the n_e enhancement will be discussed; possibilities include removal of residual OH groups and diffusion of Al atoms into Zn sites in the ZnO lattice. The rate-limiting and only thermal (180 ^oC) step of this thin film production process is the ALD, which may be expedited and conducted at lower temperature due to recent advancements in high-throughput ALD,⁵ or else replaced with a rapid liquid-phase coating technique.

References:
1. Liu, D. & Kelly, T. L. Nature Photon. 2014, 8, 133.
2. Pu, Y. et al. ACS Appl. Mater. Interfaces. 2015, 7, 25373.
3. Thimsen, E. et al. Nat. Commun. 2014, 5, 5822.
4. Gaspera, E. D. et al. Adv. Funct. Mater. 2015, 25, 7263.
5. Choi, H. et al. J. Vac. Sci. Technol. A 2016, 34, 01A121.

The light-emitting electrochemical cell (LEC) is a surface-emitting, thin-film device, which for the end user appears similar to the more well-established organic light-emitting diode. One distinguishing feature is, however, that the active material of an LEC is electrochemically doped in-situ, so that a p-n junction doping structure can form during the initial operation.[1] This in-situ transformation process paves the way for the employment of air-stabile materials for all of the constituent device materials (including the cathode) and for the utilization of a relatively uneven and single-layered active material.[2] These are important characteristics, as they pave the way for a low-cost and scalable solution-based fabrication process under ambient air, and a recent cost analysis indicates that such LEC devices can become highly competitive with both incumbent and emerging emissive technologies.[3] Here, we present our recent work on the development of fabrication processes of LEC devices using the deposition techniques of slot-die coating,[4] spray-coating,[5] and inkjet printing.[6] The slot-die coated devices were fabricated on plastic substrates mounted on a rotating wheel with a 1 meter circumference, and the fabrication steps comprised the sequential slot-die coating of a ZnO cathode ink, an active-material ink, and a PEDOT-PSS anode ink. It is notable that the entire fabrication was executed under ambient air, and that the fabricated flexible devices featured bidirectional emission.[4] The spray-coating process was developed in order to fit the specific requirements of the LEC technology (and was therefore coined as “spray-sintering”), and it has delivered uniform light-emission from 400 cm2 large-area flat surfaces as well as highly complex-shaped surfaces, such as a stainless-steel fork and a highly porous copy paper.[5,7] We have also used the spray-sintering technique for the demonstration of emissive textiles [8] and large-area signage devices[5]. For the realization of high-resolution static emission patterns, we have instead turned to inkjet printing, with which we have been able to attain signage patterns with a resolution of 170 ppi from bilayer devices.[6] We will also present recent results on the development of metal-free LEC devices,[2] and devices that deliver a combination of fast turn-on kinetics, high efficiency and long operational lifetime.[9]
References
[1] Matyba, P. et al. Nature Material, 2009, 8, 672.
[2] Matyba, P. et al. ACS Nano, 2010, 4, 637.
[3] Sandström, A. et al. Energy Technology, 2015, 3, 329.
[4] Sandström, A. et al. Nature Communications, 2012, 3, 1002.
[5] Sandström, A. et al. Advanced Materials, 2014, 26, 4975.
[6] Lindh M. et al. Small, 2014, 10, 4148.
[7] Asadpoordarvish, A. et al., Advanced Functional Materials, 2015, 25, 3238.
[8] Lanz, T. et al. Flexible and Printed Electronics, 2016, 1, 025004.
[9] Mindemark, J. et al., Chemistry of Materials, 2016, 28, 2618.

Roll-to-roll compatible processes are opening up the new opportunity for high throughput and cost-efficient manufacturing of electronics and other required functionalities. Extending the continuous roll-to-roll manufacturing approach as far as possible in the manufacturing process to assembly and bonding, the manual assembly and handling phases can be almost fully eliminated. Modern assembly and bonding machines, such as EVO2200, enable component bonding on flexible substrates in high throughput roll-to-roll process using conductive adhesives.
There are needs to build up large area flexible lighting elements to be applied as bendable forms. Organic LED (OLED) technology is promising option to produce large area, uniform and flexible lighting element. Flexible OLED structure lifetime, efficiency and luminous flux output, however, are still modest when compared to inorganic LED performance. We have utilised hybrid integration approach in which silver ink printed plastic substrates have processed by roll-to-roll screen printing pilot machine. Silver ink printed substrate is equipped next with inorganic LEDs using either isotropic conductive adhesive (ICA) or anisotropic conductive adhesive (ACA) by EVO2200 bonding machine. ICA adhesive is typically used with packaged components and ACA with non-packaged devices or chip-scale packaged (CSP) components.
We have designed and implemented several different large area flexible lighting element demonstrators. Luminous flux density value of 11900lm/m² has achieved with system based on 3535 SMD LEDs operated at 25mA. The main limitation for large area lighting element manufacturing is that web width is limited to 200 mm in roll-to-roll bonding machine. Due to the fact that assembly and bonding process is performed by roll-to-roll process, the element length can be theoretically as long as is the length of the printed web. In practise most important factors limiting practical element length are resistivity of printed tracks and size of bonded components. Maximum length of manufactured lighting element based on printed conductive tracks and bonded LED components so far has been 3 meters. Manufactured lighting demonstrators include elements equipped with RGB and RGBW LEDs, also.
Heat management and sealing processes have developed towards roll-to-roll compatibility. Heat management structures include heat spreaders, thermal vias and thermal slugs. Thermal via structures have been processed in roll-to-roll process using CO2 laser. Thermal slug structures have showed best thermal performance and processed structures so far have characterised to possess total thermal resistivity of 90°K/W, when LED thermal pad size area has been 1.34mm² and intrinsic thermal resistivity of LED component 28°K/W. LED foil with assembled components have been over moulded in roll-to-roll compatible process with thermoplastic polyurethane elastomer providing efficient against environmental stresses for components and adhesive joints.

Organic photodiodes (OPDs) are characterized by chemical tunability, mechanical flexibility and low-cost solution processing that makes them attractive for application in imaging and color detection, medical sensing and optical communication. Distinction of spectral selectivity of nearby OPD pixels is the key requirement for these applications. Today the main approach for its realization is tuning the absorption spectrum of the donor/acceptor photoactive layer components. The bottleneck of the current approach is the limited availability of narrowband absorbing materials with charge transport properties that lead to high quantum efficiency. Processing compatibility to avoid layers or/and pixels mixing during the solution deposition also plays an important role on the selection of photoactive materials. In this work, we describe a novel pixel concept and demonstrate an all-printed full-color 2D OPD array. In this approach we use both sides of flexible substrates to combine a broadband OPD and two wide range absorbing filters. The filter-OPD configuration utilizes the substrate as a separator between the single-photoactive layer OPD array and the filters. This physical separation allows solution processing of the filters regardless of the orthogonality of solvents and electrical properties of filter materials. The printing process is compatible with flexible substrates and roll-to-roll (R2R) fabrication. Layers are deposited in air using surface-assisted blade coating (Adv. Mater. 2015, 27, 6411–6417), screen-printing and spray coating. The deposition and patterning techniques are selected based on the required final film thickness. The broadband (from 350 to 750nm) bulk heterojunction (BHJ) photodetector shows external quantum efficiency (EQE) up to 40% (at -4V) and low dark current 0.5 nA/cm². The developed broadband OPD array combined with [N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and Poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) filters selectively senses red, yellow (a combination of green and red light), and white light (a combination of red, green and blue light). The pixels photoresponse was recorded and used to reconstruct RGB colored light showing only 5% deviation from the real values. We will discuss the details of the fabrication process of flexible imager arrays together with pixels performance and RGB color sensitivity.

We implement a smart electrochromic plastic window using a flexible organic power transistors prepared with roll-to-roll compatible printing techniques. This innovative transistor is able to drive large currents while handling the thermal aspects in operation together with other organic printed electronics technologies such as large area organic photovoltaics(OPV) and large area electrochromic (EC) displays. We find especially that an elevated operational temperature is beneficial for the transistor characteristics.

The footprint of organic electronic technologies is important when united in complex circuitry. We present flexible organic power transistors prepared by fast (20 m min−1) roll-to-roll flexographic printing of the drain and source electrode structures, with an interspace below 50 um, directly on polyester foil. The devices have top gate architecture and were completed by slot-die coating of the organic semiconductor poly-3-hexylthiophene and the dielectric material polyvinylphenol before the gate was applied by screen printing. We explore the footprint and the practically accessible geometry of such devices with a special view toward being able to drive large currents while handling the thermal aspects in operation together with other organic printed electronics technologies such as large area OPV and large area EC. We find especially that an elevated operational temperature is beneficial with respect to both transconductance and on/off ratio. We achieve high currents of up to 45 mA at a temperature of 80 °C with an on/off ratio of 100 which is sufficient to drive large area organic electronics such as an EC device powered by OPV devices that we also demonstrate. EC materials can change their transparency when an external voltage is applied. Such materials have interesting applications in windows. Thus, one can imagine a window in an office or a greenhouse which automatically pulls the shade by making itself darker, when the temperature gets too high.

Francesco Pastorelli, Thomas M. Schmidt, Markus Hösel, Roar R. Søndergaard, Mikkel Jørgensen and Frederik C. Krebs, " The Organic Power Transistor: Roll-to-Roll Manufacture, Thermal Behavior, and Power Handling When Driving Printed Electronics", Volume 18, Issue 1, pages 51–55, January 2016, doi: 10.1002/adem.201500348

Most organic light emitting diode (OLED) structures are based on indium tin oxide (ITO) as the transparent electrode, which is inherently limited due to its brittleness, expense and its low-throughput method of production. While its relatively high conductivity (sheet resistance in the order of 5 Ω/sq.) is suitable for small area devices, it becomes a limiting factor in larger scale, where higher conductivity is essential. It is therefore desirable to use other approaches to replace ITO in order to address these concerns.^[1]
One of these is represented by economically and ecologically viable printing of metal nanoparticle inks. Selective drop-on-demand inkjet printing allows direct-write material deposition, low processing temperatures and flexible digital computer-aided design production, requiring no masks or lithographic pre-patterning of substrates, and delivers high enough resolutions for transparent conducting electrodes (TCEs) in lighting applications. Inkjet-printing can also be upscaled and transferred to a roll-to-roll process for printed electronics, which can produce a large throughput of cells or large area devices.^[2]
However, especially when inkjet-printing these metal nanoparticles as bottom electrodes, the typical feature height of printed structures of several 100 nm tend to exhibit a rough surface with many spikes or defects. This can lead to shorts in the device and/or high leakage currents after subsequent overcoating of the solution-processed organic layer.
We therefore present the process development of a solution-processed TCE based on inkjet-printed silver grids, by firstly reducing the printed line height <100 nm by using UV-O₃ surface treatment to achieve a low grid line height of ~80 nm, which enables full coverage by the above lying PEDOT:PSS buffer layer. The completed ITO-free OLEDs show comparable luminance efficiency and power efficiency values to reference devices based on ITO and near identical efficiencies at low luminance values.^[3]
In a second step, we demonstrate planarised embedded inkjet-printed metal grids, which leads to an increase in device efficiency of 250 % compared to ITO and exhibits an outstanding high efficiency of up to 9.4 cd/A.^[4] The results highlight overall printing processing parameters and the implementation of novel metal materials and architectures in printed electrodes for high performance solution-processed OLEDs will be discussed.

[1] J. D. Servaites, S. Yeganeh, T. J. Marks, M. A. Ratner, Adv. Funct. Mater. 20 (2010) 97.
[2] R. R. Søndergaard, M. Hösel, F. C. Krebs, J. Polym. Sci. B 51 (2013) 16.
[3] F. Hermerschmidt, I. Burgués-Ceballos, A. Savva, E. D. Sepos, A. Lange, C. Boeffel, S. Nau, E. J. W. List-Kratochvil, S. A. Choulis, submitted.
[4] L. Kinner, S. Nau, K. Popovic, S. Sax, I. Burgués-Ceballos, F. Hermerschmidt, A. Lange, C. Boeffel, S. A. Choulis, E. J. W. List-Kratochvil, submitted.

The large volume production of plastic electronic devices by solution based roll-to-roll (R2R) manufacturing technologies is a crucial step towards the commercial success of the organic electronics industry. Deposition of all functional structures from solution eliminates the need for expensive vacuum processing methods. Devices like organic light emitting diodes (OLEDs) consist of a stack of several functional layers. In this contribution, approaches are presented for the solution processed R2R production of both patterned and homogenous layers of functional materials for flexible OLED devices on foils. Furthermore the development of a R2R coating line with two slot die coating stations will be discussed which is capable of applying uniform layers up to 20 m/min.

Switchable glasses, which are capable of adjusting their light transmission between opaque and transparent modes in response to external stimuli, have attracted considerable interest due to their potential uses, such as light diffusion in light emitting diode (LED) devices, backlight units of liquid crystal displays (LCDs), solar controls, and personal privacy demands. A range of approaches have been developed to assign dynamic optical properties to glasses. Chromogenic materials, liquid crystals and electrophoretic suspended-particle devices have been developed, and are now commercially available
Here, Transparent, flexible composite films with switchable haze are presented that respond stably and rapidly to applied bias. The composite film is based on the laminated structure of all flexible materials, such as the polyethylene terephthalate substrate, graphene, paraffin-polydimethylsiloxane (P-PDMS) organogel and PDMS overlayer stacked in order. Upon applying a bias, the graphene is Joule-heated, leading a microstructural transformation of paraffin impregnated in the PDMS matrix, which in turn causes the modulation of light scattering. While the total transmittance is maintained above 90% in the visible range, transmission haze of the film can be controlled over the range from 0.5 to 85% with a low applied voltage and power consumption of 18 V and 0.33 W/cm2, respectively. Because of the presence of an over-coating layer of PDMS, stable and reliable operation of the composite film is achieved for number of switching cycles. The advent of a highly transparent optical film with haze controllability that is made possible by this work can be used as a diffusive film to enhance the light-trapping properties for photovoltaics, and attachable films with controllable clarity on a window for ensuring personal privacy.

Inspired by kirigami paper-cutting art, here we introduce a nanocomposite manufacturing technique for adaptive optical elements, exemplified by strain-tunable diffraction gratings. An engineered pattern of slits in layer-by-layer assembled nanocomposites from plastics, metals and carbon nanotubes enables stretchable optical diffraction gratings with over 100% range of period tunability. These reconfigurable optical gratings enable dynamic beam steering and can serve as a foundation for low-cost implementations of adaptive optics. The angular range of beam steering can be as large as 6.5 degrees for 635nm laser beam as compared to ~1 degree in previously reported surface-grooved elastomer gratings and ~0.02 degree in MEMS gratings. The engineered micro/nanostructures lend to high degrees of tunability, simplicity and reliability of the devices. The results suggest opportunities for developing advanced adaptive optics and optoelectronics through kirigami-inspired engineering.

Metamaterials and metasurfaces allow the engineering of properties that not exist in nature. This has attracted significant research attention with potential applications such as negative index of refraction, perfect lenses and optical cloaking. The fabrication of optical/infrared metasurfaces (nanoscale features over large areas), remains a large obstacle for real-world applications. For example, while techniques such as E-beam lithography (EBL) or Focal ion beam (FIB) milling are viable for laboratory scale demonstrations they are cost-prohibitive for practical applications over meter squared areas. Microsphere PhotoLithography (MPL) is a flexible, cost-effective and high-throughput micro-/nano- fabrication technique. MPL utilizes microspheres as microlenses to focus UV radiation to a photonic nanojets within the photoresist. This differs from NanoSphere Lithography (NSL) that utilizes micro/nanospheres as a physical shadow mask during evaporation/etching. In MPL, the microspheres are self-assembled into Hexagonal Close-Packed (HCP) patterns. When flood illuminated with normally incident collimated UV radiation, a simple HCP array of holes is transferred to the pattern. The size of these holes is dependent on the dose and can be used to fabricate simple resonators. This presentation studies the response of the MPL process to off-normal incidence illumination. The photonic jet can be steered around the HCP unit cell to define more complicated patterns. The off-axis MPL fabrication technique is demonstrated for the fabrication of various functional metasurface frequency selective designs including tripole, loops, and split-ring resonators. These are characterized using FTIR and shown to match well with Finite Element Method (FEM) simulation using ellipsometrically measured material properties, despite the metasurfaces having a polycrystalline microstructure.

The fabrication occurs using a Computer Numerical Controlled (CNC) tip-tilt stage that enables rotation of 360° in horizontal plane and tilt of ±90° from horizontal plane. The exposed photoresist is functionalized using standard e-beam evaporation and lift-off. With off-axis illumination, the offset of the disks from the microsphere center is nearly linear with respect to the tilt angle regardless of sphere diameter and exposure dosage, while the diameter of holes scales linearly with exposure dosage regardless of tilt angle. The periodicity is adjustable by changing the size of the microspheres. The substrate is also tunable to materials with higher refractive index like silicon or germanium. These characteristics makes the off-axis highly flexible.

For the realization of next generation Ultra High Definition Televisions (UHD-TVs) both quantum dots (QDs) and organic light emitting diodes (OLEDs) will play a crucial role. Both materials are extremely sensitive to the presence of water vapor, so high grade barrier encapsulation films (down to 10^-6 g/m² day) are mandatory to achieve the 10 years lifetime at room temperature required by commercial products. In this paper the latest advances in R2R CVD processing will be illustrated, showing the impact on optical and barrier performance of substrate type, single layer and fully integrated multilayer CVD based film stacks. Architectural solutions to challenges inherent in moving from lab & pilot scale manufacturing to high volume production will be illustrated. Particular attention will be given to defect detection process, critical for achieving high production yields and enabling the upcoming wave of flexible electronic devices.

Multilayer stack of alternating inorganic/organic layers from nanoscales to microscales play a pivotal role in devices in terms of insulators for transistors, active layers for solar cells, passivation layers for organic devices. Generally, vacuum processes are frequently used for the deposition of inorganic layer. However, unlike the inorganic layers, organic layers are usually implemented via solution-based processes (e.g. spin-coating). Hence, in order to deposit alternating organic-inorganic layers, the substrate must be loaded into and vented out from a vacuum chamber repeatedly, which is extremely laborious. This process incompatibility between the inorganic and organic layers lowers the process productivity and throughput.
In this regard, initiated chemical vapor deposition (iCVD) has several advantageous characteristics that make it a powerful candidate for depositing organic layer. Inherited from the conventional CVD process, the solvent-free process provides highly pure, pinhole-free thin film and exhibits outstanding step coverage. The process temperature of the vapor-phase method is in the range of 10 – 60 °C, minimizing thermal damage to organic electronic devices. In addition, iCVD is highly promising for scale-up and mass-production. Furthermore, the similarity of the iCVD and atomic layer deposition (ALD) processes has enabled the integration of two processes as a one-step deposition system, which is capable of depositing iCVD polymer and ALD inorganic layers in a single chamber geometry.
In this presentation, the iCVD and ALD processes are integrated into one reactor to deposit multilayer stack of inorganic/organic layers. Analysis of the iCVD and ALD layers deposited in the proposed integrated system confirmed that the properties of the films are equivalent to those deposited in separate iCVD and ALD systems. The integrated system permits a simple alternation between the deposition processes to produce organic-inorganic multilayers, without breaking the vacuum. The processes can be optimized independently, and the study demonstrated that the deposition of one layer does not alter the properties of the other layers during the alternating depositions.
As demonstrations, we fabricate multilayer-stacked thin-film encapsulation (TFE) layer and a bilayer-structured hybrid dielectric layer with ultrathin thickness (< 15 nm) for OTFTs. The combination of iCVD and ALD deposition processes produced organic-inorganic multilayers with outstanding barrier, optical, and mechanical properties. It also turned out that hybrid dielectric layer generally exhibited reduced hysteresis and interfacial trap densities of OTFTs, which resulted in substantial improvement of the device performances. Coupled with the process temperature of lower than 90 °C, the integration of iCVD and ALD in a one chamber will be beneficial to design the various kinds of flexible, soft electronics onto the thermally vulernable substrates.

Large-area applications of 2D materials such as membranes and barrier films require means of cost-effective roll-to-roll manufacturing. We present the design and use of a split zone CVD reactor for roll to roll synthesis of 2D materials by chemical vapor deposition. The reactor configuration consists of an annealing and growth zone separated by a narrow slit through which the catalytic flexible metallic substrate (foil) passes from one end of the reactor to the other. We present the design of this system as guided by flow simulations. Using the system constructed in our laboratory, we demonstrate synthesis of uniform, high quality graphene at speeds up to 500 mm/min, specifically for membrane and barrier applications. A detailed investigation into the process parameters that influence the growth of graphene on a moving substrate allows us to identify process optimization techniques for roll to roll synthesis and subsequent processing for manufacturing of films with tailored nanoscale porosity. We reflect on the scalability of this process, and general principles for roll-to-roll CVD of other 2D materials.

References:
Kidambi et al. (Manuscript in preparation)
Polsen et al. Scientific Reports (2015) DOI: 10.1038/srep10257
Kobayashi et al. Applied Physics Letters (2013) DOI: 10.1063/1.4776707
Kidambi et al. Nano Letters (2013) DOI: 10.1021/nl4023572

Flexible electronic devices, fabricated on bendable and light-weight substrates, have gained significant attention in recent years. As opposed to using the rigid, brittle and highly expensive single-crystalline semiconductor wafers, the ability to use mechanically flexible, alternate low-cost substrates to develop opto-electronic devices offer the potential for large-area, scalable manufacturing of cost-effective devices with a broad range of new applications. For high performance devices single-crystal films are needed and for scalable roll-to-roll (R2R) processing flexible inexpensive substrates are essential. However, methods to grow single-crystalline epitaxial semiconductor films directly on low-cost, flexible substrates by R2R processing have remained challenging so far.
In this work, we demonstrate a method to grow a wide range of technologically important semiconductor films (Ge, Si and III-Vs) with near-single-crystal structure and excellent opto-electronic properties on low-cost metal substrates. Ion-beam assisted deposition (IBAD) was used to obtain highly-oriented single-crystalline-like films on polycrystalline flexible metal substrates. Long lengths of IBAD MgO films were developed on flexible Hastelloy (C-276) metal foils and flexible glass by continuous R2R process to obtain biaxially-textured MgO template. Successive buffer layers of LaMnO₃ and CeO₂ were deposited using R2R sputter systems to obtain the preferred lattice matching conditions for subsequent Ge growth. Meter lengths of biaxially-textured Ge films on textured metal substrates were deposited which were then used as substrates for Si and III-V GaAs thin film growths using chemical vapor deposition.
We will report on the development of single-crystalline-like Si and SiGe films using inductively-coupled plasma chemical vapor deposition (ICP-CVD) on flexible substrates. Biaxially textured Si and SiGe thin films with strong (004) out-of-plane orientation and sharp in-plane texture (< 2 degrees) were obtained at a wide range of growth temperatures (700-900 C). Raman spectroscopy showed complete crystalline nature with sharp peak-width comparable to wafer. High carrier mobilities of over 200 cm²/V-s has been achieved in Si films on metal substrates, which can be used to fabricate high performance thin film transistors for flexible electronics applications.
We will also report on the development of epitaxial GaAs and related III-V films on Ge template on IBAD textured flexible metal substrates using metal-organic chemical vapor deposition (MOCVD). Strong biaxial texture, (004) orientation, room-temperature photoluminescence and high electron mobilities exceeding 1200 cm²/V-s were achieved in GaAs films. Controllable n and p-type doping from 10¹⁶-10¹⁹ cm^-3 has also been achieved. The potential device applications (PV, MOSFETs, etc) of high opto-electronic quality III-V films on low-cost metal substrates will be demonstrated.

Since its discovery in 1968, nanocrystalline silicon, a biphasic material comprising of an amorphous hosting matrix with embedded silicon nanocrystals, attracted considerable attention due to the superior stability and carrier mobility with respect to its amorphous counterpart in combination with a comparable high absorption coefficient. Additional flexibility arises from the tunable optical, electronic and light emitting properties of the nanocomposite, depending on the size and amount of the crystallites inclusions. Standard synthesis routes suffer however from high processing temperatures, low yield and lack of morphology control, hindering a technological breakthrough in fields such as thin films transistors and photovoltaics. Despite a high number of fundamental investigations on NCM materials properties, a comparatively smaller attention was dedicated to the means of their application. In this work we demonstrated the possibility of transferring fundamental findings into cluster assembled semiconductor-based devices by means of a deposition techniques capable of (i) directly depositing NCM as a dense thin film with high throughput on appropriately large areas, (ii) controlling NCM fundamental compositional characteristics like crystalline fraction and nanocrystals grain size, (iii) depositing NCM on a wide variety of substrates, including thermo-labile polymeric materials.
We present a large area (100 cm²), ultra-high yield (up to 1 μm min^-1 or 300 mg h^-1), plasma-based deposition technique (Nanoparticles Jet Deposition) of nanocrystalline silicon cluster-assembled thin films compatible with thermolabile substrates. The process is based on the segmentation of the gas phase material synthesis in two steps: (i) nanoclusters synthesis and growth control in a non-thermal dusty plasma environment, allowing in-flight, low temperature crystallization; (ii) nanoparticles-assembled films ballistic growth via super sonic jet acceleration. Nanocomposite materials showing densities up to 50% of bulk silicon can be directly synthetized with crystalline fractions ranging from 0 to 72% and the nanocrystalline inclusion sizes can be tuned in the range from 2 to 5.5 nm with subnanometers size distributions Time of flight spectroscopy is employed to investigate nanoparticles-assembled films charge carriers transport mechanisms in anomalous dispersive regime. Mobility up to 2 × 10^-5 cm V^-1 s^-1 was observed, reaching the highest reported mobility for a silicon nanoparticles-assembled film deposited at low-temperature. An ultra-high yield synthesis route producing high quality silicon-based thin films at polymer-compatible temperatures represents the first step for a powerful integration of the well-known inorganic semiconductors technology with emerging trends in freestanding nanocrystals synthesis.

Many applications that utilize nanomaterials in manufactured products require that the particles be deposited as films or coatings. These may be, for example, thermal barrier coatings on high-temperature parts, active layers in electronic devices, optical layers in laser Bragg mirrors, or biocompatible coatings for medical applications. In all cases, theses coatings should be able to be deposited rapidly over large areas, have a uniform and controllable thickness, and their constituent particles should maintain their unique nano-scale properties.

Present nanomaterial films developed in laboratories are often incompatible with roll-to-roll (R2R) technology and are unable to be reproduced on an industrial scale; the manufacturing methods are inherently nanomaterial and substrate specific. This specificity results in manufacturing equipment that is expensive or offers limited utility. We propose an advanced nanomaterial film manufacturing technology based on hypersonic particle deposition (HPD) that overcomes these deficiencies.

HPD begins by aerosolizing a nanomaterial using any desired technique, from atomizing a nanoparticle-laden solution to feeding nanoparticle-precursor gas into a plasma. The aerosolized material is fed into the HPD system, which consists of two chambers separated by a slit-shaped nozzle, with the bottom chamber held under vacuum (0.01–1 Torr). The nanomaterial is accelerated to a velocity of several hundred meters/second as it and the aerosol background gas are forced through the nozzle, resulting in the formation of a curtain of nanoparticles directed into the downstream chamber. A substrate is passed through the curtain, and the nanomaterial collides with and adheres to the substrate, forming a thin coating.

We will showcase our efforts to develop a large-scale HPD system compatible with R2R technology. As a test case, we will demonstrate our ability to deposit CdSe nanoparticle filmss on multiple substrates to form quantum- dot- enhanced films(QDEFs) used in liquid crystal displays without the use of a polymer matrix and silicon nanoparticle films of controllable porosity for use as antireflective coatings. .

Initial data will show the ability to deposit films 100 nm to 5000 nm thick with +- 4% non-uniformity over a 4-inch wide substrate with porosities ranging from 75% to 99%. Further, our QDEFs will show that particles maintain their nano-properties after deposition with red (636 nm) and green (533 nm) quantum dot photoluminescence FWHMs of less than 35 nm and 27 nm, respectively.

While considerable progress has been made in the fabrication of flexible and stretchable circuits and displays, flexible batteries needed to power these devices remain challenging and underpowered. Recent, progress in this field includes the use of polymer substrates, composite membranes, paper and yarn based electrodes.[1,2] However, many of these designs suffer from fast-capacity decay, limited flexibility, poor thermal management, and high weight.[3,4]

To address these problems, we have designed new electrodes which alleviate stress from the electrochemical active material during bending. To achieve this, we populate a flexible current collector with 3D CNT microstructures[5,6] on which we decorate the electrochemical active material.[7] The base of these CNT structures is anchored in a conductive polymer collector electrode and is as small as possible to avoid stress transfer from this substrate to the active material. The CNT structures then widen into a cone shape to have a large surface area to coat the active material. The unpatterned CNT forests readily crack when they are bent, while our new patterned design does not. Even when folding our electrodes to radii as small as 300 μm no cracks were observed. This radius was limited by our ability to handle the thin films rather the electrode material itself. These electrodes were tested for both half coin cell type as well as full flexible cells. We found that this battery architecture not only imparts excellent flexibility, but also high rate (20A/g), cycling stability (over 500 cycles at 1C with capacity retention over 70%).[7] The electrode fabrication process, which starts by lithographically patterning catalyst particles into rings from which CNTs are grown by thermal chemical vapour deposition (CVD). The CVD process results in the formation of micro-cylinders that each consists of thousands of vertically aligned CNTs. These cylinders are transformed into cones using elasto-capillary aggregation. Next, the cones are transferred by contact printing[8] to a flexible conductive film, with a yield close to 100%.



References:

[1].T. Someya, Nat. Mater. 2010, 9, 879.
[2].R. C. Webb, A. P. Bonifas, A. Behnaz, Y. Zhang, K. J. Yu, H. Cheng, M. Shi, Z. Bian, Z. Liu, Y.S. Kim, W.H. Yeo, J. S. Park, J. Song, Y. Li, Y. Huang, A. M. Gorbach, J. A. Rogers, Nat. Mater. 2013, 12, 938.
[3].J. Ren, Y. Zhang, W. Bai, X. Chen, Z. Zhang, X. Fang, W. Weng, Y.
Wang, H. Peng, Angew. Chemie Int. Ed. 2014, 53, 7864.
[4].L. Hu, H. Wu, F. La Mantia, Y. Yang, Y. Cui, ACS Nano 2010, 4, 5843.
[5].M. De Volder, S. H. Tawfick, R. H. Baughman, A. J. Hart, Science 2013, 339, 535.
[6].M. De Volder, S. H. Tawfick, S. J. Park, D. Copic, Z. Zhao, W. Lu, A. J. Hart, Adv. Mater. 2010, 22, 4384.
[7].Shahab Ahmad, D. Copic, C. George and Michael D. Volder, Adv. Mater.
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[8].Z. Rong, Y. Zhou, B. Chen, J. Robertson, W. Federle, S. Hofmann, U.
Steiner, P. Goldberg-Oppenheimer, Adv. Mater. 2014, 26, 1456.

In recent years, organic and metal-oxide semiconductors have captured a great deal of attention for their potential as active materials in smart sensor systems, on grounds of their solution processability, potentially low manufacturing cost, and possibility of deployment in a variety of non-traditional situations. While much sought-after, complementary integration on organic-only or oxide-only platforms has been impaired by the low performance of n-type organic semiconductors, and the challenges associated with p-type metal-oxide semiconductors. Concurrently, a hybrid approach has come to the fore as the ideal combination of active materials, featuring a p-type-organic/n-type-metal-oxide semiconductor pair.^1–3
Relevance to real-world applications demands low-voltage operation, which is crucial for battery-powered and portable electronics. Addressing this very challenge, here we show that it is possible to achieve low-voltage and high-performance circuit operation on foil via solution-processed complementary hybrid integration. This is demonstrated specifically with two-stage differential amplifiers, namely core analog circuits relevant to a wealth of signal conditioning and sensing applications.
In this presentation I will discuss our innovative route to solution-processed low-voltage integration of organic and metal-oxide semiconductors on foil, and I will present an in-depth characterization of the resulting differential amplifiers. Superior performance is achieved in a number of fundamental metrics, such as differential gain, and reduction of power supply voltage (down to 5V) and power dissipation. Differential gains greater than 1000 (60dB) with a power supply at below 8V constitute, to the best of our knowledge, the highest performance of any organic or metal-oxide differential amplifier demonstrated to date. Therefore, new exciting opportunities are opening up for solution-processed analog circuits targeting battery-powered applications.

1 K. Myny, S. Smout, M. Rockele, A. Bhoolokam, T. H. Ke, S. Steudel, K. Obata, M. Marinkovic, D.-V. Pham, A. Hoppe, A. Gulati, F. G. Rodriguez, B. Cobb, G. H. Gelinck, J. Genoe, W. Dehaene and P. Heremans, in 2014 IEEE International Solid-State Circuits Conference Digest of Technical Papers (ISSCC), IEEE, 2014, vol. 57, pp. 486–487.

2 K. Myny, M. Rockele, A. Chasin, D. V. Pham, J. Steiger, S. Botnaras, D. Weber, B. Herold, J. Ficker, B. Der Van Putten, G. H. Gelinck, J. Genoe, W. Dehaene and P. Heremans, IEEE Trans. Electron Devices, 2014, 61, 2387–2393.

3 V. Pecunia, K. Banger, A. Sou and H. Sirringhaus, Org. Electron., 2015, 21, 177–183.

Stainless steel substrates enable a combination of low cost, flexibility, durability, high processing temperatures, and sub<100 um thickness making it well suited for sheet based and roll-to-roll processing. NFC (13.56 MHz) based circuits using high performance polysilicon TFTs on steel sheets have been manufactured using a hybrid printed process in a production environment. The process scheme utilizes a hybrid, additive materials approach encompassing non-traditional steps such as slot die coating and screen printing of silicon and dopant inks to enable a high throughput, low cost, manufacturing flow. In this presentation, the approach for migrating from a sheet-based hybrid process flow to a R2R-based process is described. A comparison of substrate choices and considerations for R2R process integration is presented. A sensitive electrical method for evaluating the feasibility of R2R-based process integration schemes and materials selection is presented. MIM capacitor leakage, TFT device characteristics, NFC circuit performance, and defect density considerations are shown as a function of steel substrate bending, down to a diameter of 20 mm. Electrical characteristics and optical inspections show no measurable change to insulator characteristics, demonstrating a high degree of flexibility and overall device and process capability for R2R processing.

Remarkable optoelectronic properties coupled with low temperature solution process-ability and environmental abundance of the precursor materials makes hybrid organic-inorganic metal halide perovskites an attractive alternative for low-cost next-generation photovoltaic cells. Efficient carrier transport and low internal losses in these materials lead to high open-circuit voltages and outstanding solar power conversion efficiencies. However, to realize large-scale deployment, emerging thin film technologies must achieve high efficiencies using high-throughput manufacturing techniques. Currently, the majority of perovskite PVs in research reports are fabricated by a combination of spin coating, dip coating, and thermal evaporation. These techniques are not easily scalable and therefore hamper the commercialization prospect of perovskite technology.
Inkjet printing of hybrid organic-inorganic perovskites (e.g., CH₃NH₃PbI₃) offers a promising approach for low-cost, scalable manufacturing of future thin-film solar cells. In this work, we develop a process for printing perovskite solar cells from a single printable precursor solution and report the influence of precursor solution chemistries and key printing parameters on the CH₃NH₃PbI₃ film formation, thickness, morphology and homogeneity as well as the corresponding photovoltaic performances.
To synergize with the advantages of inkjet printing in cost and scalability, we demonstrate printing onto graphene electrodes. Presently, indium tin oxide (ITO) is the most widely used material for transparent electrodes. However, the brittleness and cost of ITO motivate demand for an alternative in low cost, flexible applications. Excellent mechanical properties, chemical inertness, and high optical transparency make graphene a promising candidate with the potential to complement or replace traditional transparent conductors. Continuous CH₃NH₃PbI₃ films with controlled morphology were achieved via engineering of the ink-jet solution and 11% efficient devices with graphene electrodes on a flexible substrate were demonstrated. These advancements are important steps towards realizing low-cost scalable production of flexible perovskites solar cells.


*YS and AO contributed equally to this study

Small-molecule based photovoltaic devices have recently demonstrated performance nearly on par with the more extensively studied polymer based devices. Small-molecules have considerable advantages in terms of scaling the synthesis and material purity. However, small-molecule based inks tend to be more difficult to optimize. The technique of solvent vapor annealing (SVA) has recently been shown to be an effective means of optimizing film morphology/device performance. While simple rules of thumb have emerged (good solvents tend to achieve poorer results than moderate solvents), the precise mechanism of SVA improvement has not been established. We present the results of SVA studies of bulk heterojunction (BHJ) solar cells based on the acceptor phenyl-C 71 -butyric-acid-methyl ester ([70]PCBM) and the small molecule donors benzodithiophene terthiophene rhodamine (BTR) or 7,7’-(4,4-bis(2-ethylhexyl)-4 H-silolo[3,2-b :4,5- b’]dithiophene-2,6-diyl)bis(6-fluoro-5-(5’-hexyl-[2,2’-bithiophen]-5-yl)benzo[c][1,2,5]thiadiazole) (p-DTS(FBTTh₂)₂). Using in-situ x-ray scattering, both wide angle for characterization of crystallinity and small angle for characterization of phase purity and domain length scale, we examine the detailed kinetics of film modification by both a good solvent (chloroform, CF) and a moderate solvent (tetrahydrofuran, THF). The SVA evolution is directly contrasted to thermal annealing. For BTR devices, we find the degree of crystallinity comparable for all techniques. However, SVA results in greater phase purity than TA. SVA in CF leads to large domain structures, unfavorable for OPV performance, while THF leads to more optimal domain purity and size. The evolution of the microstructure can be directly related to nucleation density (determined by the degree of solvent dissolution of small seeds) and molecular mobility (determined by the plasticization of the mixed, disorders regions). For p-DTS(FBTTH₂)₂) devices, we remarkably find that SVA leads to the ability to maintain power conversion efficiencies over 8% for film thicknesses up to 300 nm. Compared to the traditional solvent-additive optimized device, SVA achieves higher phase purity without excessive phase ripening. Impedance spectroscopy establishes that the increase in functional film thickness is due to a significant decrease in carrier recombination.

Studying the gelation processes of conjugated optoelectronic polymers provides crucial fundamental insight into the assembly in active layers of organic electronic devices due to the correlation between the experimentally observed sol-gel transition and many common solution based fabrication techniques. This because the morphology of the percolated network structures formed via the molecular assembly that occurs during gelation governs device performance in many conjugated polymer based active layers. Thus, understanding the evolution of structures during gelation is needed to rationally improve device reliability and performance. Moreover, there exist environmental factors, including exposure to ambient light, that can alter the gelation process and these factors must be correlated to structure and performance to improve device reliability. Thus, we report the results of a series of ultra small angle and small angle neutron scattering experiments to probe the impact of light exposure on the temperature-driven gelation process of the conjugated photoactive polymer poly(3-hexylthiophene-2,5-diyl) (P3HT).
These results demonstrate that exposure to white light significantly retards the growth of conjugated polymer microstructures during gelation. More importantly, these results indicate that ignoring illumination conditions throughout organic electronic fabrication processes risks producing inconsistent and non-reproducible active layer architectures and ultimately endangers dependable device performance.

Inkjet printing of organic photovoltaics (OPV) with customary images is highly desirable in terms of improving the aesthetics of the modules and reducing production complexity. Most of the work on inkjet printed OPV has relied on PEDOT:PSS as transparent electrode material combined with highly conductive opaque metal grids to lower its series resistance. These metal grids however create visual obstruction to the supposedly freeform shapes. On the other hand, silver nanowire (AgNW) electrodes have already been demonstrated to have excellent properties in various OPV geometries and architectures. Due to the high aspect ratio of AgNWs however, inkjet printing of such material has proven to be challenging and often resulted in compromises such as low optical transparencies and high processing temperature.
In this work, we show for the first time inkjet printing of AgNW electrodes exhibiting excellent electrical (sheet resistance <20 Ω/sq) and optical (weighted transmittance 94 % with reflectance of glass deducted) properties. The electrodes were optimized by investigating the effects of various parameters such as the ink formulation, printing resolution and printing direction on the spatial and orientation distribution of the AgNW network. This in turn, allows us to optimize the directional conductivity and optical transmittance for the specific application in organic photovoltaics. With optimized AgNW electrodes, OPV devices are inkjet printed from small scale to larger modules that exhibit excellent performance and good optical properties (weighted transmittance 31 %). First highly efficient semitransparent small scale (0.1cm²) OPV are inkjet printed with power conversion efficiencies (PCE) over 6.3%. Then fully inkjet printed semitransparent organic solar cells with power conversion efficiencies (PCE) of 4.3 % for 1 cm² are demonstrated. This will be compared with cells of same device structure except with conventional PEDOT:PSS/silver metal grids electrode to illustrate the aesthetical and performance enhancements. Furthermore, visually non-obstructive, inkjet printed semitransparent OPV modules of 4 cm² with PCE of 4.3 % and 88cm² human portrait OPV modules with PCE of 1.6% are demonstrated for the first time.
Finally we will apply this electrode on organic light emitting diodes to demonstrate its versatility on other organic electronic devices.

The transfer of well working lab scale organic solar cells, to entirely printed, high efficiency modules has so far been proven to be a difficult challenge. One of the many hidden obstacles in the up-scaling process is the formation of a well working and visually non-obstructive series interconnection between the single solar cells.
In this work, we compare different interconnect strategies and processing methods, highlighting their advantages as well as limitations for scalable high throughput roll-to-roll (R2R) solar module fabrication. Using a combination of slot die coated layers and high resolution ultrafast LASER patterning (sub 10 micron resolution; high processing speeds up to 4 m/s), we demonstrate flexible and semitransparent organic solar modules with a geometrical fill factor (ratio between active area and total area of the module - GFF) of > 95 %, which is one of the highest values reported in literature, with a power conversion efficiency (PCE) of over 4 % on an area of 70 cm². By cross section images, we provide in depth analysis of the interconnect regions and contact formation. Balancing the achieved result with the production complexity, we evaluate the potential of this method for large volume inline processing.
As an alternative route we demonstrate for the first time digitally printed solar module interconnects. Using a novel strategy with a printed highly conductive silver line which penetrates all other solar cell layers, a bottom-up electrical series connection of the single cells is formed. By varying the height of the silver line, we show how the resistance at the interconnect region can influences the PCE. Using this method, we demonstrate solar modules reaching a GFF close to 90 % and PCE of over 4 % on large area. Furthermore, we show how the unique advantages of digital printing can be used to overcome design restrictions which limit the solar module layout to simple geometric patterns such as rectangles. By inkjet printing electron blocking, hole blocking as well as active layer, we demonstrate an arbitrary shaped semitransparent highly efficient P3HT:PCBM solar module in the form of a 84 cm² portrait. With the ease to change designs and the medium to high processing speeds up to 10 m/min we evaluate the potential of digitally printed modules for mass production.
Finally, we summarize the capabilities of both module strategies highlighting their chances to enter today’s highly customized markets like building integrated photovoltaic (BIPV) and consumer electronics.

Photodetctors based on organic materials have attracted attention due to their wide spectral response, low dark current density, efficient photoresponse and fast response time. In particular, bulk heterojunctions (BHJs) has been exploited in organic photodetectors (OPD) due to their high photocarrier generation efficiency and simplified solution-based fabrication. However, the co-existence of the donor and acceptor materials at both cathode and anode interfaces can lead to high dark currents due to formation of the shunt currents between anode and cathode. Dark current suppression can be achieved, in principle, by controlling donor/acceptor (D/A) segregation using a double-layered active layer structure. To fabricate the bilayer structure, “orthogonal” solvents are required for each material to avoid resolvation of an already-deposited layer. Typical polymer and fullerene derivative materials can be easily dissolved in halogenated solvents such as chlorobenzene (CB), dichlorobenzene (DCB) or dichloromethane (DCM). So far, the most popular method to realize the bilayer of the heterojunction was successive spin-coating deposition of the solution of the electron acceptor material dissolved in DCM on polymer film since the solvent typically has lower solubility with polymer materials. However, this method can easily allow partial penetration of the each material to counter-electrodes forming macroscopically undesirable films.
To address above mentioned problems we develop a novel double transfer stamping (DTS) method to realize interdiffused bilayer heterojunction (BiHJ) OPDs with well-defined electron donor and acceptor layers at the metal interfaces, leading to dark current suppression. The approach leads to a device having both a low dark current and high photoresponsivity through optimization of the metal / organic interface and segregation of materials within the active layer by subsequent thermal annealing. Dark current densities as low as 7.7 nA/cm² and 60 % of external quantum efficiency are achieved with a calculated specific detectivity of 4.8 x 10¹² cmHz^1/2W^-1 at a reverse bias of 1.5 V at a wavelength of 546 nm. The organic photodiodes also show a linear dynamic range of > 120 dB.

Transparent and conducting oxide (TCO) materials gain widespread use in most technological applications in recent years. They are used in optoelectronic applications like lasers, LEDs, solar cells, energy saving windows and touch panel displays. Fluorine doped tin dioxide (FTO) is one of the most common TCO materials for thin film and dye sensitized solar cells (DSSC). Production methods of FTO include mostly vacuum based techniques like PVD or CVD methods. Spray deposition is a versatile and low cost technique for deposition of oxide materials which does not require costly vacuum systems or sophisticated production equipments. Ultrasonic spraying has been gaining popularity against conventional spraying which reduces chemical consumption and provides ability of precise control of spraying pattern over large area substrates.
Fluorine doped thin dioxide (FTO) thin films were produced via conventional spray pyrolysis and ultrasonic spray pyrolysis (USP) using alcohol based solutions. The prepared films were compared in terms of crystal structure, morphology, surface roughness, visible light transmittance and electronic properties. Investigating the grain structures and morphologies, the films prepared using ultrasonic spray method provided relatively larger grains and due to this condition, carrier mobilities of these films exhibited slightly higher values. Deposition conditions, precursor and chemical recipe of the coating solutions (F/Sn ratios) were optimized for high performance FTO thin film TCOs. Industrial sized FTO films of 10x10 cm showed sheet resistance values down to 4 ohm/sq at a thickness of 800 nm and visible light transmission of 70% at 550 nm. DSSC cells and 10x10 cm modules were prepared using commercially available and USP deposited FTO/Glass substrates and solar performances were compared. It is observed that there exists no remarkable efficiency difference for both cells and modules where module efficiency of the USP deposited FTO glass substrates is 3.06% compared to commercial substrate giving 2.85% under identical conditions. We demonstrated that USP deposition is a low cost and versatile method of depositing commercial quality FTO thin films on large substrates employed in large area DSSC modules or other thin film technologies.

High-performance metallic transparent conductors (TCs) are demonstrated by integrating Ag nanowire (NW) networks into microscale Ag grid structures. Highly conductive Ag grids are fabricated via direct imprinting of thermally reduced Ag NPs using a reservoir-attached mold. In the reservoir-attached mold, a grid-patterned cavity is connected to a macroscale cavity (reservoir). The reservoir has a large cavity volume that leads to decrease unwanted residual layers within the grid spacings by providing thinner liquid film. The reservoir undergoes a large volume reduction during mold deformation, which improves ink filling within the grid-patterned cavity by deformation-driven ink injecting. After Ag NW spin-coating on the metal girds, the hybrid metallic TCs show a sheet resistance (R_s) of < 2 Ω/sq and a transmittance (T) of 85 % at 550 nm, superior to the corresponding values of Ag NW networks (R_s of 21 Ω/sq at a similar T). The hybrid metallic TCs based on Ag NW-grid are successfully transferred, and embedded to a transparent and flexible polymer matrix. The embedded hybrid metallic TCs, which show a reasonable electromechanical stability, are applied to fabricate flexible organic solar cells as anode electrodes.