Rodrigo Noriega, University of Utah
Jonathan Rivnay, Northwestern University
Elizabeth von Hauff, Vrije Universiteit Amsterdam
Ni Zhao, Chinese University of Hong Kong
The University of Utah, Department of Chemistry
EP05.01: Mixed Ionic-Electronic Conduction—Materials and Characterization
Monday PM, November 26, 2018
Hynes, Level 2, Room 208
8:00 AM - *EP05.01.01
Local Structure and Counter-Ion Properties Control Ion Uptake in Organic Electrochemical Transistors
University of Washington1Show Abstract
Organic electrochemical transistors (OECT) are of interest for applications in biochemical sensing and signal transduction across the biological/digital divide. The excellent performance of conjugated polymers in these applications is due to the ability of the polymer to accommodate ionic countercharge throughout the transistor volume. The resulting volumetric capacitance which allows for very large modulations of the charge density in the transistor channel and large transconductance values. Combining OECT measurements on different polymers with different counter ions, we study how both polymer morphology and the chemical nature of the counter ions affect ion uptake and coupling between ionic and electronic transport. Furthermore, we use electrochemical strain microscopy (ESM) to probe local swelling resulting from ion uptake, and correlate ion uptake with both polymer structure and the chemical properties of the ions, providing microscopic insight into these processes that lead us to propose new material design rules.
8:30 AM - EP05.01.02
Operando X-Ray Scattering Reveals Ion-Induced Structural Changes During Electrochemical Gating of Poly(3-hexylthiophene)
Elayne Thomas1,Michael Brady2,Hidenori Nakayama1,Bhooshan Popere1,Rachel Segalman1,Michael Chabinyc1
University of California, Santa Barbara1,The Advanced Light Source, Lawrence Berkeley National Laboratory2Show Abstract
The semicrystalline nature of most semiconducting polymers complicates the relationship between morphology and electronic conduction. In order to increase their electrical conductivity, charge carriers are introduced into conjugated polymers by extrinsic dopants, usually by introduction from solution or by infiltration from a vapor. In this case, the dopant molecule, now ionized, is the counterion to the charged backbone. There is currently little understanding of how these ions interact with the amorphous and crystalline regions of the semiconductor to achieve the observed large changes in electrical conductivity.
To address the question of how ions interact with these distinct phases, we have explored the evolution in morphology and optoelectronic properties of a conjugated polymer in an organic electrochemical transistor. By using a novel polymeric ionic liquid (PIL) as the gate insulator, we carry out for the first time operando studies capturing the structural evolution in poly(3-hexylthiophene) (P3HT) during electrochemical gating by X-ray scattering. PILs contain one ion covalently bonded to the polymer backbone and one ion that is mobile, which allows for control of counterion diffusion as well as low-voltage device operation. From these experiments, we find that negatively-charged ions from the dielectric first infiltrate the amorphous regions of the semiconductor, and penetrate the crystalline regions at a critical carrier density of 4 × 1020 cm–3. Upon infiltration, the crystallites expand by 12% in the alkyl stacking direction and compress by 4% in the π–π stacking direction. The stark change in crystal structure of P3HT correlates with a sharp increase in the effective carrier mobility. Complementary UV-visible spectroscopy reveals that holes induced in P3HT first reside in the crystalline regions of the polymer, which verifies that a charge carrier need not be in the same physical domain as its associated counterion. Our results provide a comprehensive view of doping in P3HT which challenges the assumption that trap filling is the sole mechanism to justify the non-linear trend in electrical conductivity with carrier density.
8:45 AM - EP05.01.03
Conjugated Polyions—Charged Semiconducting Polymers Processed from Protic Solvents
Ryan Chiechi1,Lambert Jan Anton Koster1,Nutifafa Doumon1,Gang Ye1
University of Groningen1Show Abstract
Semiconducting conjugated polymers have found applications in field-effect transistors, sensors, solar cells, etc. In essentially any application that requires a semiconducting material, the semiconducting material can be replaced with a properly-designed conjugated polymer, endowing a device with the useful properties of polymers such as solution-processing, mechanical compliance, thinness and light weight. However, the solutions from which thin-films of conjugated polymers are cast contain very small amounts of polymer, on the order of tens of milligrams per milliliter. The nonpolar nature of pi-conjugated moieties means that high-quality films can only be cast from solvents that are either difficult or impossible to work with at scale.
One approach to creating conjugated polymers that can be processed from “green” solvents is to decorate them with charged pendant groups to form conjugated polyeletrolytes that can be dissolved in polar, protic solvents like water or methanol. However, designing conjugated polyeletrolytes that are both processable and retain high carrier mobility is challenging because of the disparate physical properties of the backbone and pendant groups. This amphiphilic nature drives the polymer chains to self-assemble such that, in polar solvents, the hydrophobic backbone chains pack together and are shielded by a shell of ionic pendant groups to minimize unfavorable solvent interaction. These protein-like aggregates are carried into the films, leading to poor pi-pi contact.
Our approach is to place closed-shell charges into the backbones of conjugated polymers to match the ionic character of the pendant groups such that the backbone is directly solubilized by polar solvents. The resulting conjugated polyions are intrinsic semiconductors; they are not bipolaronic and are EPR silent. Their band-gaps can be tuned via common push-pull strategies and they form high-quality films with good carrier mobility from polar, protic solvents. The cations in the backbone are generated from pre-polymers by the loss of methanol under acidic conditions. Thus, we can process high-quality thin-films from wet formic acid, which is non-toxic, non-flammable and is already used industrially at scale.
9:00 AM - *EP05.01.04
Polar and Reactive Side Chain Functionalization of Conjugated Polymers for Redox and Bio-Electronic Applications
Georgia Institute of Technology1Show Abstract
Conjugated polymers provide a unique encompassing set of structurally tunable optical, electronic transport, and redox properties that allows their present and potential use in a host of applications which span field effect transistors, light emitting diodes, solar cells and photodetectors, and electrochromism, along with batteries, supercapacitors, and bio-electronics. Processing of these materials is carried out using a variety of solution methods including spin-coating, spray-coating, blade-coating, slot die coating and ink jet printing. The ability to process these polymers from environmentally benign solvents and aqueous solutions is highly advantageous for possibilities in large scale roll-to-roll processing. Maintaining competitive electronic properties while achieving aqueous solubility is difficult for several reasons. 1) Materials with polar functional groups that provide aqueous solubility can be difficult to purify and characterize. 2) Many traditional coupling and polymerization reactions cannot be performed in aqueous solution. 3) Ionic groups, though useful for obtaining aqueous solubility, can lead to a loss of solid-state order as well as a screening of any applied bias. In this lecture, we will address how side chain polarity, from charge neutral ether and ester functionality to ionic functionality, impacts not only processing, but also charge transport, redox switching and optical properties. As an alternative, a multistage side-chain cleavage approach will be presented that allows a functional group to be used for its intended purpose, then removed once the functionality becomes unnecessary. Through the attachment of multistage sidechains, conjugated materials can be synthesized, characterized, and purified in organic solvents, converted to a water-soluble form for aqueous processing, and brought through a final treatment to leave behind the desired electronic material as a solvent-resistant film.
10:00 AM - *EP05.01.05
Semiconducting Polymer for Bioelectronics and Field Effect Transistors
King Abdullah University of Science and Technology1,Imperial College London2Show Abstract
The evolution of organic electronics has now reached the commercial phase, with the recent market introduction of the first prototypes based on organic transistors and organic solar cell modules fabricated from solution. Understanding the impact of both the organic semiconductor design and processing conditions, on both molecular conformation and thin film microstructure has been demonstrated to be essential in achieving the required optical and electrical properties to enable these devices. Polymeric semiconductors offer an attractive combination in terms of appropriate solution rheology for printing processes, mechanical flexibility for rollable processing and applications, but their optical and electrical performance requires further improvement in order to fulfil their potential. Synthesis of conjugated aromatic polymers typically involves carbon coupling polymerisations utilising transition metal catalysts and metal containing monomers. This polymerisation chemistry creates polymers where the aromatic repeat units are linked by single carbon-carbon bonds along the backbone. In order to reduce potential conformational, and subsequently energetic, disorder due to rotation around these single bonds, an aldol condensation reaction was explored, in which a bisisatin monomer reacts with a bisoxindole monomer to create an isoindigo repeat unit that is fully fused along the polymer backbone. This aldol polymerization requires neither metal containing monomers or transition-metal catalysts, opening up new synthetic possibilities for conjugated aromatic polymer design, particularly where both monomers are electron deficient. Polymers with very large electron affinities can be synthesised by this method, resulting in air stable electron transport, demonstrated in solution processed organic thin film transistors. We present an electrical, optical and morphology characterisation of polymer thin films, illustrating structure-property relationships for this new class of polymers. Organic electrochemical transistors (OECTs) have been shown to be promising devices for amplification of electrical signals and selective sensing of ions and biologically important molecules in an aqueous environment, and thus have potential to be utilised in bioelectronic applications. The sensitivity, selectivity and intensity of the response of this device is determined by the organic semiconducting polymer employed as the active layer. This work presents the design of new organic semiconducting materials which demonstrate significant improvements in OECT performance, through operation in accumulation mode, with high transconductance and low operating voltage.
10:30 AM - *EP05.01.06
Organic Electrochemical Transistors—Developments on Modelling the Transient Response and on Device Fabrication
University of Sao Paulo1Show Abstract
Organic Electrochemical Transistors (OECTs) have recently been the focus of great attention due to their ability to support both ionic and electronic conduction and their successful application as highly-sensitive biosensors and neuromorphic devices. In the first part of my talk, I will discuss a universal model for the transient drain current response in OECTs. Using equivalent circuits and semiconductor charge injection physics, the model is able to reconstruct the drain current in OECT devices, is applicable to both plain and membrane-functionalized devices, and allows one to extract useful impedances of any system from only a single transient measurement. For the second part of my talk, I will present a general method and accompanying guidelines for fabricating both non-aqueous and aqueous based OECTs using water-insoluble hydrophobic semiconducting polymers. By taking advantage of the interactions of semiconducting polymers in certain organic solvents and the formation of a stable liquid-liquid interface between such solvents and water, we successfully fabricated OECTs with high transconductance, ON/OFF ratios of 106, and enhancements in stability. Using the model discussed in the first part of the talk, key fundamental properties of both the device and active channel materials were extracted, including volumetric capacitance and intrinsic hole mobility. Finally, the benefits of using liquid-liquid interface OECTs to measure bacterial membrane disruption will be briefly discussed.
11:00 AM - EP05.01.07
In Situ Methods for Understanding Charge Transport in a Conducting Redox Polymer
Mia Sterby1,Rikard Emanuelsson1,Maria Strømme1,Martin Sjödin1
Uppsala University1Show Abstract
Organic materials can be used to ensure sustainable electrical energy storage, but since organic molecules are generally insulating conducting additives are commonly used to ensure electrical conductivity throughout the material. A different approach is to use conducting redox polymers (CRPs). CRPs consist of a redox active pendant group, used for its high capacity, attached to a conducting polymer backbone. The CRP presented here is aimed to be used as the positive electrode in a water-based organic battery.
In this work we employ the well-studied conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) with a quinone pendant group, a combination that we have proven can work in an all-organic proton battery.1 Quinones constitute an attractive class of molecules as they possess a high charge storage capacity, show reversible redox chemistry, and are naturally occurring, e.g., in the electron transport chains in respiration and in photosynthesis. The aim of the study is to understand the charge transport properties of the CRP.
The CRP studied is characterized by various in-situ electrochemical methods including conductance, Quartz Crystal Microbalance (QCM), UV-vis and Electron Paramagnetic Resonance (EPR). Based on the results the electron and ion transport during electrochemical redox conversion will be discussed.
1. Emanuelsson, R.; Sterby, M.; Strømme, M.; Sjödin, M., An All-Organic Proton Battery. J. Am. Chem. Soc. 2017, 139 (13), 4828-4834.
11:15 AM - *EP05.01.08
Conductive Polymer Electrodes for Biosensors and Energy Conversion
University of Arizona1Show Abstract
Electron transfer is a ubiquitous chemical reaction in energy and biology. Controlling interfacial electron transfer rates is critical to maximizing device efficiencies in electrochemical technologies including redox-flow batteries, chemical sensors, bioelectronics, and photo-electrochemical devices.
Conductive polymer electrodes offer the possibility to control redox properties through synthesis and processing, if critical structure-property relationships are understood. Importantly, these semiconductors demonstrate a hybrid electronic-ionic conduction mechanism, and thus, have unique electrochemical behaviors relative to classical inorganic semiconductor electrodes.
This talk will provide new insights into the mechanism of charge transfer at conductive polymer/liquid interfaces. A mathematical framework will be demonstrated using a modified Marcus-Gerisher model that enables prediction of rate constants from simple film properties. Experimental evaluation of potential-dependent rate constants will be demonstrated. Results will be contextualized in electrochemical devices.
EP05.02/BM07.02: Joint Session: Bioelectronic Active Materials
Monday PM, November 26, 2018
Sheraton, 2nd Floor, Constitution B
1:30 PM - *EP05.02.01/BM07.02.01
Interacting Ion and Electron Currents
Swansea University1Show Abstract
Ionic and electronic conduction mechanisms are underpinned by fundamentally different physics . For example, ions diffuse through a conducting matrix via centre of mass transport that can be described by classical processes. Electrons and holes are quantum mechanical entities characterised by delocalisation, tunnelling or hopping. These fundamental differences impose radically different length-and-time-scales on ionic and electronic conduction – and generally speaking the solid-state physics of ions and electrons have remained two very different fields requiring different skill sets . However, bioelectronics, where a central challenge is the transduction between ion and electron currents, is a scientific collision point between the two worlds.
In my talk I will summarise the major differences between ionic and electronic solid state electrical conduction. I will also describe methods that can probe the relevant time-and-length scales in order to identify and disentangle the native signatures of each carrier type [3, 4]. A number of model systems and devices will be exemplified that allow the study of ion and electron conduction processes, and indeed provide a means to test prototypical concepts in transduction and bioelectronic logic interfaces [5, 6].
 N. Amdursky, E. Glowacki & P. Meredith, Advanced Materials, 2018, (in press)
 P. Meredith, C. J. Bettinger, M. Irimia-Vladu, A. B. Mostert and P. E. Schwenn, Reports on Progress in Physics, 2013, 76, 034501
 A. B. Mostert, B. J. Powell, F. L. Pratt, G. R. Hanson, T. Sarna, I. R. Gentle and P. Meredith, Proceedings of the National Academy USA, 2012, 109, 8943-8947
 A.B. Mostert, S.B. Rienecker, C. Noble, G.R. Hanson & P. Meredith, Science Advances, 2018, 4(3), eaaq1293
 M. Sheliakina, A.B. Mostert & P. Meredith, Materials Horizons, 2018, 5, 256-263
 D.J. Carrad, A.B. Mostert, A.R. Ullah, A.M. Burke, H.J. Joyce, H.H. Tan, C. Jagadish, P. Krogstrup, J. Nygard, P. Meredith & A.P. Micolich, Nanoletters, 2017, 17(2), 827-833
2:00 PM - EP05.02.02/BM07.02.02
The Device Physics of Organic Electrolytic Photocapacitors—From the Nanoscale to the Single Cell Level
Vedran Derek1,Marie Jakesova1,Tobias Cramer2,Marek Havlicek3,David Rand4,Yael Hanein4,Daniel Simon1,Magnus Berggren1,Fredrik Elinder1,Eric Glowacki1
Linkoping University1,Università di Bologna2,Czech Metrology Institute3,Tel Aviv University4Show Abstract
We have recently developed the organic electrolytic photocapacitor (OEPC), a nanoscale optoelectronic device for eliciting action potentials in neurons. Herein, we cover in detail the physical mechanisms behind the charge generation and dynamics of charging and capacitive coupling in these devices using optoelectronic/electrochemical measurements combined with simulation and modeling. Electrochemical impedance measurements allow corroboration of these models, and reveal the nature of photocapacitive and photofaradaic effects in the devices. Using scanning probe microscopy techniques, we have evaluated the mechanical properties of the nanocrystalline films, finding relatively low Young’s moduli in the range of 500 MPa. In order to take a reductive approach compared with previous measurements of neurons and electrogenic tissues, we have validated the performance of OEPCs using nonexcitable cells, xenopus laevis oocytes. We find rapid membrane potential changes in the range of tens to hundreds of millivolts are induced by OEPC devices, showing extremely effective capacitve coupling and explaining previous findings of action potential generation. The overall result of our work is a fuller physical and mechanistic understanding of this novel device platform, and a roadmap for guiding future development.
2:15 PM - EP05.02.03/BM07.02.03
The Design of Air Stable, Redox Active Conjugated Polymers and Their Applications in Accumulation Mode OECTs
Alexander Giovannitti1,Reem Rashid2,Jenny Nelson1,Iain McCulloch1,Jonathan Rivnay2
Imperial College London1,Northwestern University2Show Abstract
Organic electrochemical transistors (OECTs) are receiving a great deal of attention due to the ability to efficiently transduce biological signals. The working principle of OECTs relies on the modulation of the conductivity of an organic semiconductor, which can be modified by applying a potential at the gate electrode and driving electrochemical redox reactions in aqueous solution (doping/de-doping of the organic semiconductor). OECTs can either be operated in accumulation1–3 or depletion mode4 where the operation in accumulation mode has the advantage of lowering the operational voltage and therefore improve the power consumption of the device (device is in an off state rather than an on state when no gate voltage is applied). Recently, high performing OECT materials have been reported based on electron rich alkoxybithiophene copolymers which show low oxidation potentials in aqueous electrolytes and enable OECT operation at low voltages. 2
However, one drawback of these easily oxidizable polymers is that the copolymers can become oxidized by reactions with oxygen from ambient air. This result in the formation of p-doped polymers and superoxide anions (O2-) where the latter is a reactive radical and might cause harm to biological systems or degrade the organic semiconductor. As a result of this oxidation reaction, a constant gate voltage would need to be applied to keep the material in its neutral state (and the device off).
We will present the development of an air-stable conjugated polymers based on donor-acceptor type copolymer. The copolymer shows reversible redox reaction at potentials below 0.3 V vs Ag/AgCl. When exposed to aqueous ambient conditions, the polymer does not become oxidized. Long-term stability tests were carried out where devices were exposed to ambient conditions for more than 6 months with no sign of degradation. The polymer shows a good stability when charged with up to one hole per repeat unit (polaron) with transconductances in the range of 80 S/cm (at -0.7 V). This work demonstrate the importance of chemical design strategies for the development of accumulation mode OECT materials to mitigate reactions with oxygen in aqueous electrolytes and ambient conditions.
1. Inal, S. et al. Adv. Mater. 26, 7450–7455 (2014).
2. Giovannitti, A. et al. Proc. Natl. Acad. Sci. 113, 12017–12022 (2016).
3. Nielsen, C. B. et al. . J. Am. Chem. Soc. 138, 10252–10259 (2016).
4. Khodagholy, D. et al. Nat. Commun. 4, 2133 (2013).
2:30 PM - *EP05.02.04/BM07.02.04
Polythiophene Derivatives as Mixed Organic Ionic and Electronic Conductors
University of Washington1Show Abstract
Mixed organic ionic and electronic conductors are being explored for a wide range of applications, from bioelectronics to neuromorphic computing, artificial muscles and energy storage applications. These materials exploit the simultaneous transport properties of ionic and electronic carriers to enable novel device functions. Recently, polymer semiconductors have received significant amounts of attention because of their flexibility, biological compatibility and ease of fabrication. These materials, particularly thiophene-based polymers such as poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS) and related derivatives, have demonstrated significant enhancements in performance in a relatively short amount of time, with transconductance values of PEDOT:PSS transistors surpassing those achieved even with graphene.
Through our NSF Designing Materials to Revolutionize and Engineer our Future (DMREF) award with researchers at Cornell University and the University of Chicago, we have been investigating the synthesis of ethylene-glycol functionalized polythiophenes, their thin film morphology, and their ionic and electronic conductivities, and comparing against theoretical predictions. In this talk, the effect on the density of the ethylene-glycol side chains and their pattern of placement on ionic conductivity will be discussed.
3:00 PM - EP05.02/BM07.02
3:30 PM - *EP05.02.05/BM07.02.05
Mixed Conductivity in Conducting Polymer Thin Films
University of Stuttgart1Show Abstract
This talk will give an overview about our recent activities on electronic and ionic conductivity in conjugated and redox polymer thin films with different molecular architectures. Preparation of films is done either by electropolymerization or solution deposition followed by morphology tuning, e.g. by solvent vapor annealing.
We are particularly interested in three-dimensional architectures based on branched monomers such as terthiophenes (3T) or triphenylamines (TPA). TPA redox moieties are useful to allow for electrochemical or chemical crosslinking of as-deposited films. Both, with TPA redox polymers and with polymers which bear TPA as pending redox moieties of linear polythiophenes we could perform successful crosslinking and simultaneous doping of polymer films. The films provide very high stabilities with high electronic conductivities as evidenced by cyclic voltammetry coupled with in-situ conductance measurements and four-point-probe measurements. In the case of 3T we have reported on homopolymer and copolymer films of 3T and ethylenedioxythiophene which allow polymer-analogous reactions to induce ionic functionalities, thereby creating branched conjugated polyelectrolyte films., 
To get a better understanding on mixed conductivity in polymer films, we have recently performed a study on electronic and ionic conductivity of linear conjugated polyelectrolytes by impedance spectroscopy and dc-measurements. The clear dependence of the conductivities as function of humidity and degree of doping will be discussed in the talk in more detail.
 G.L. Schulz, S. Ludwigs, Adv. Funct. Mater. 27, 2017, 1603083.
 O. Yurchenko, J. Heinze, S. Ludwigs, Chem. Phys. Chem. 11, 2010, 1637.
 P. Reinold, K. Bruchlos, S. Ludwigs, Polymer Chemistry 8, 2017, 7351.
 M. Goll, A. Ruff, E. Muks, F. Goerigk, B. Omiecienski, I. Ruff, R.C. González-Cano, J.T. Lopez Navarrete, M.C. Ruiz Delgado, S. Ludwigs, Beilstein J. Org. Chem. 11, 2015, 335.
 T.V. Richter, C. Bühler, S. Ludwigs, J. Am. Chem. Soc. 134, 2012, 43.
 R. Merkle, P. Gutbrod, P. Reinold, M. Katzmaier, R. Tkachov, J. Maier, S. Ludwigs, Polymer 132, 2017, 216.
4:00 PM - *EP05.02.06/BM07.02.06
Glycolated Thiophene Oligomers and Polymers for Bioelectronic Applications
NIL Technology ApS1Show Abstract
4:30 PM - EP05.02.07/BM07.02.07
Organic Electronics for Neuromorphic Computing
Yoeri van de Burgt1
Eindhoven University of Technology1Show Abstract
Neuromorphic computing could address the inherent limitations of conventional silicon technology in dedicated machine learning applications. Recent work on silicon-based asynchronous spiking neural networks and large crossbar-arrays of two-terminal memristive devices has led to the development of promising neuromorphic systems. However, delivering a parallel computation technology, capable of implementing compact and efficient artificial neural networks in hardware, remains a significant challenge. Organic electronic materials offer an attractive alternative to such systems and could provide neuromorphic devices with low-energy switching and excellent tunability, while being biocompatible and relatively inexpensive.
This talk describes state-of-the-art organic neuromorphic devices and provides an overview of the current challenges in the field and attempts to address them1. We demonstrate a novel concept based on an organic electrochemical transistor2 and show how some challenges in the field such as stability, linearity and state retention can be overcome3.
Furthermore, we investigate chemical doping mechanisms in the active material for improved material functionality and demonstrate that this device can be entirely fabricated on flexible substrates, introducing neuromorphic computing to large-area flexible electronics and opening up possibilities in brain-machine interfacing and adaptive learning of artificial organs.
1 van de Burgt et al. Nature Electronics, 2018
2 van de Burgt et al. Nature Materials, 2017
3 Keene et al. J Phys D, 2018
4:45 PM - EP05.02.08/BM07.02.08
Anisotropic Conducting Polymer Films for Bioelectronics
Patricia Jastrzebska-Perfec1,Georgios Spyropoulos1,Jennifer Gelinas1,Dion Khodagholy1
Columbia University1Show Abstract
Anisotropic conductive films, which consist of electrically conductive particles dispersed in nonconductive media, are increasingly being applied to establish high-density electrical bonds between electronic boards and chips. However, current anisotropic composites utilize metallic particles, often nickel and epoxy-based media, that require high thermocompression energy for bonding. Therefore, they have limited applicability in thin-film, conformable, and plastic-based devices that are used in bioelectronic applications. Furthermore, these materials are not biocompatible, significantly limiting their use in biological systems. We hypothesized that replacing the metallic particles with conducting polymer particles combined with a biocompatible nonconducting matrix would address this limitation. We developed a novel anisotropic conducting polymer (ACP) consisting of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) conducting polymer particles dispersed in a matrix of crosslinked chitosan (CS). To determine the permeability of PEDOT:PSS to CS, we characterized the resistances of thin CS-based films sandwiched with PEDOT:PSS and gold pads. We investigated the particle size, structure, density and distribution of pure PEDOT:PSS particles and PEDOT:PSS-coated CS particles. The anisotropy was defined by the ratio of horizontal and vertical impedance between interconnects. We benchmarked the anisotropy of the developed ACPs by geometrically varying an array of gold electrodes. The final ACP, which was created at 70°C with minimal pressure, yielded anisotropy of 105-106. The ACP was then used to maintain precise connections between a high density conformable implantable neural probe and back-end electronics. It enabled complete chronic in vivoimplantation of these electronics with minimal encapsulation layers, highlighting applicability for use in bioelectronic and clinical devices
EP05.03: Poster Session I: Ion, Electrons and Photons in Organic Materials and Devices
Tuesday AM, November 27, 2018
Hynes, Level 1, Hall B
8:00 PM - EP05.03.01
Temporal Analysis of Transient Electroluminescence to Study the Effect of Charge Traps in Organic Light Emitting Diode
Sohyeon Bae1,Jooyoun Kang1,Jung Son1,Gyeong Woo Kim2,Kyung Min1,Soohwan Sul2,Woo Jeon2,Jaeduck Jang2,Gyeong-Su Park1,Jay Shin2,Jang Hyuk Kwon3,Seong Kim1
Seoul National University1,Samsung Advanced Institute of Technology2,Kyung Hee University3Show Abstract
A comparative study was carried out for pristine vs. degraded organic light emitting diode (OLED) devices regarding their luminescence characteristics using time-resolved electroluminescence (TREL). Notable changes were observed in the temporal form of the TREL curve upon materials degradation, which was found to be due to the trapped charges formed during the OLED operation. The TREL decay time of degraded OLED was found to be longer than that of pristine OLED due to the excitons produced by weakly bound charges trapped in the organic layer that are released by thermal energy even without applying the voltage pulse. On the other hand, the onset time of luminescence was found to be shorter due to the excitons from strongly bound charges that are released by the application of the voltage pulse. We demonstrated that TREL can be effectively used to identify different typesof exciton and to investigate the luminescence mechanisms of a light-emitting device.
8:00 PM - EP05.03.02
Enhancement of N-Type Organic Field-Effect Transistor Performances Through Surface Doping with Aminosilanes
Nara Shin1,2,Jakob Zessin1,2,Min Ho Lee3,Mike Hambsch1,2,Stefan Mannsfeld1,2
TU Dresden1,Center for Advancing Electronics Dresden2,Leibniz Institute for Solid State and Materials Research Dresden3Show Abstract
Organic field-effect transistors (OFETs) have received considerable attention as essential components of organic electronics, which have the advantage of large-area scalability and processability over inorganic based transistors. However, organic semiconductors (OSCs) in OFETs have relatively low electrical transport properties that need to be improved before realization in commercial applications. In order to improve the electrical transport properties dopants are commonly introduced to bulk or surfaces of OSC films. In contrast to bulk doping, surface doping (SD) achieved by the addition of dopants to top of film surfaces can lower the adverse effects on electrical properties seen in bulk doping. Previous SD studies have shown enhancement in device performances but did not clearly investigate the SD mechanism systematically.
The SD efficiency can vary greatly depending on the properties of the OSCs, dopants, and especially the film conditions since the doping effect can be sensitive to the film structure. Therefore, we investigate the SD mechanism through a comparative study of two different OSC materials, small molecule PTCDI-C8 and polymer N2200, doped with two kinds of aminosilanes, and various thicknesses and grain sizes of deposited films to find the optimum SD condition. We characterized the doped films and OFETs by using AFM, Grazing-incidence X-Ray Diffraction, Infrared spectroscopy, electrical measurements, etc.
As a result, higher doping efficiency showed in the doped PTCDI-C8 FETs than N2200 FETs due to the difference of intrinsic OSC properties such as its open film morphology. Additionally, the SD efficiency is decreased with increasing thickness and grain size of the OSC films. The more electron donating groups the dopant has, the lower doping concentration is needed to reach the same optimized value. Importantly, we find that there are two doping concentration regimes. In low doping concentrations, the dopants primarily contribute to the increase in mobility. In higher doping concentrations, the dopants also enhance the threshold voltage. Furthermore, the SD process does not adversely affect other OFET properties such as the on-off ratio.
Therefore, our results demonstrate that the properties of OSCs, dopants and particularly the film conditions must be considered in order to maximize the SD efficiency for improved OFET performances.
8:00 PM - EP05.03.03
Metal Organic Frameworks in a Blended Polythiophene Hybrid Film with Surface-Mediated Vertical Phase Separation for the Fabrication of a Highly Sensitive Humidity Sensor
Young Jin Jang1,Eun Hye Kwon1,Yeong Don Park1
Incheon National University1Show Abstract
Demand for portable gas sensors capable of monitoring the atmospheric environment in daily life is growing as air pollution deteriorates. Organic field-effect transistors (OTFTs) are regarded as an ideal flexible platform for creating portable, lightweight, and robust sensor devices. OTFTs are sensitive to physical and chemical stimuli because small interactions between a semiconductor and a target analyte amplify the electrical signal of a transistor device via the field-effect mobility, drain current, and threshold voltage. However, organic transistors inevitably suffer from poor stability and bad electrical properties, resulting in a slow response and recovery of the sensor device. We attempted to address this issue by developing an OTFT-based humidity sensor, in which a humidity-capturing material was inserted into the polymeric semiconductor. In this study, a facile, reliable, fast-response, highly sensitive poly(3-hexylthiophene-2,5-diyl) (P3HT)-based humidity sensor was developed by introducing metal organic frameworks (MOFs), HKUST-1, into the semiconducting layer. HKUST-1 displayed an excellent ability to capture water molecules, thereby generating and attracting charge carriers derived from water molecules present in the active layer. The HKUST-1/P3HT hybrid film showed excellent device sensitivity with an enhanced electrical current and a threshold voltage shift as a function of the relative humidity due to the superior gas capture properties and the porosity of HKUST-1. The surface energy of the substrate altered the distribution and location of HKUST-1 in the active layer, which improved the sensitivity of the hydrophilic surface. A dynamic gas sensing test revealed that the hybrid film displayed a reliable and stable performance with fast response and recovery times. The introduction of MOFs into a conjugated polymer stabilized and sensitized the devices, providing a facile method of improving gas sensor technologies based on organic semiconductors.
8:00 PM - EP05.03.04
Tuning Electrical Properties of Phenanthroimidazole Derivatives to Construct Multifunctional Deep-Blue Electroluminescent Materials
City University of Hong Kong1Show Abstract
The maturity of longer wavelength emitters (green and red) makes it more urgent to develop high performance deep-blue emitters OLED ( organic light-emitting diodes). A blue emitters that can serve as a multifunctional material (e.g as host for the green and red courterparts) is of high interest in this field. we introduce a n-type group, TPPO (triphenyl phosphine), to the N1-position of violet-blue fluorophore phenanthroimidazole (PI) and successfully develop one deep-blue (TPAPOPPI) and two violet-blue emitters (3-CzPOPPI and CzBPOPPI) for OLEDs (organic light-emitting diodes). With highly twisted linkage, the TPPO group shows negligible influences on their photophysical properties of the new materials and the materials inherit high efficient deep-blue and violet-blue emission of the PI unit and its C2-connected arylamine skeletons. Meanwhile, TPPO group can open a new channel to transport electron. The electron injection and transport abilities of the developed emitters are enhanced. Non-doped devices using the 3-CzPOPPI and the CzBPOPPI emitters exhibit EQEmax (external quantum efficiency) of 5.08% and 4.42% with CIE (Commission Internationale de l'Èclarage) coordinates of (0.156, 0.061) and (0.157, 0.071), respectively. Similar efficiencies and even deeper blue emissions (CIEy = 0.050 for 3-CzPOPPI and 0.044 for CzBPOPPI) were observed in OLEDs with these emitters doped in 4,4’-bis(N-carbazolyl)-1,1’-biphenyl. TPAPOPPI is demonstrated to be a multifunctional deep-blue emitter and presents impressive performances when serving as non-doped (EQEmax = 6.69%, CIE: (0.152, 0.095)), doped (EQEmax = 6.61%, CIE: (0.154, 0.068)) as well as a high-performance host for yellow phosphorescent OLED. By doping