Symposium EN01—Materials for Sustainable Electronics

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During the production of organic solar cells, the exposure of constituting materials and resulting devices to light, heat, oxygen and water is a potential source of degradation. We show that thermo-oxidation of the active materials occurs upon annealing the active layer or upon stirring the active materials solutions in air at elevated temperatures. By comparing various blends of donor polymers with fullerene or non-fullerene acceptors, the fullerene is identified to be the most susceptible component to thermal oxidation in both film and solution, while the polymer remains unaffected. In both cases, the effect on the photovoltaic device performance consists predominantly in a decreased short-circuit current (J_SC), suggesting that the underlying degradation mechanism is the same in the solid state and in solution. Thermo-oxidation of the active layer during annealing of the device can be decelerated by blending nickel(II) dibutyldithiocarbamate (Ni(dtc)₂) as antioxidant additive into the active layer. While small concentrations of additive stabilize the J_SC and therefore the power conversion efficiency, higher contents negatively affect device performance. Thermo-oxidation of the active materials in solution during stirring in air at elevated temperatures can be avoided for several hours by adding as little as 0.5% of Ni(dtc)₂. The observation that the antioxidant is consumed during stabilization of the active materials suggests a sacrificial protection mechanism.

Power and space-saving in CMOS technology reached almost a dead end due to the imposed thermodynamic and quantum mechanical limitations around 2005, which necessitated a search for novel 2D materials to revive the otherwise stagnated CMOS technology to further its evolutionary trajectory. The possibility of an engineerable band gap brought semiconducting TMDC MoS₂ as one of the prominent among the 2D layered material family for photodetection and gas sensing applications. But, as the size of the 2D material devices is being scaled down to reduce the cost and power consumption, scientists encountered a serious problem with “contacts”, which are the gateway between the 2D devices and the external 3D world. The nature of the metal contact and the type of contact between the metal and 2D semiconductors play a vital role in device fabrication. Proper analysis on the local surface potential and work functions of 2D semiconducting film and contact will throw light on the best contact material for a particular semiconducting system or for a certain number of layers of 2D layered semiconducting material, as the work function of layered material, is also thickness or layer dependent.
Through this work, we will present a rather unusual photoswitching response observed in the photodetection study on silver electrode MoS₂/AlN/Si heterostructure was grown through Pulsed Laser Ablation. Two independent mechanisms have been tried to account for the dual photoswitching displayed by the symmetrical electrode device. The work function of Ag, Schottky barrier formed during Ag deposition on MoS₂, and fluctuation in the charge neutrality level of MoS₂ with stimulus wavelength are attributed to the photoswitching noticed in the visible range. Photoswitching at the NIR range of the input spectrum is primarily related to the induced plasmonic effect due to irregularly diffused silver nanoparticles into the semiconductor during thermal evaporation.

Sustainable technological development requires recycling of materials, particularly those essential for energy generation and storage, such as the lanthanides and lithium (Li). Recycling of these metals is currently not performed on a large scale, but with growth in demand, one may foresee serious shortages already by the end of the current decade.
High energy density magnets, based on alloys of Nd(+/-Pr +/-Dy)–Fe–B (Nd-alloy), are critical components of a variety of electromechanical and electronic devices. During the last decade, consumption of lanthanide (a.k.a. “rare earth”, RE, element) has risen annually by ≈30%(!!!), primarily due to increased production of hybrid and electric vehicles. Since a standard hybrid/electric automobile requires ≈5-10 kg of RE, while ≈ 40 wt % of the Nd-alloy is lost as scrap during the manufacturing process, large-scale recycling of RE has become an urgent necessity. However, recovery of RE from manufacturing scrap, and especially from end-of-life magnets, poses a difficult technical challenge. The latter requires removing the magnets from the used device, demagnetization, crushing/milling, and applying chemical processes to separate the RE from the Fe component. Demagnetization, by heating in vacuo, and crushing/milling are both costly procedures and the latter may introduce unwanted contamination. Strong acids/bases and/or corrosive melts are currently employed to extract the RE metals. Both routes produce toxic waste, for which the cost of neutralization often exceeds the value of the recovered RE. Instead, we developed an economically and ecologically friendly RE recycling process. Pulverization (decrepitation) into ~ 45mm particles is achieved by introducing atomic hydrogen into the used magnets, without the necessity for prior demagnetization, via room temperature electrolysis in a diluted NaOH solution. Separation of Fe from the RE is achieved by chlorination of the fine powder at ~ 673K, which results in sublimation of chlorides of Fe and B, leaving pure RE chloride. Chlorine gas from non-RE sublimates is recycled, while the RE chlorides may be reduced to metal via moderate temperature eutectic melt electrolysis.
Although Li-batteries initially emerged as a power source for portable devices, incorporation of Li-batteries in vehicles and industrial power banks, led to an exponential growth in the demand for lithium and cobalt. While lithium production is almost exclusively oriented towards batteries, cobalt is also an essential component of high-strength alloys and magnets, with demand for batteries beginning to compete with these traditional applications. Recovery of Li and Co from spent Li-batteries poses technical challenges. In addition to the fact that opening and crushing spent batteries may result in self-ignition, current technologies aim at Co extraction only. Many of these technologies require sequential treatment with acids and bases, producing toxic waste, or involve dumping of crushed batteries into Co-smelting ovens. In both cases, lithium ends up in compounds from which it cannot be readily recovered. We have developed an economical procedure that recovers metallic Co and Ni, and Li in carbonate form. This process is based on treating crushed, spent batteries with natural gas in a rotating kiln at 973K. Following treatment, Co and Ni may be extracted with a magnetic separator and Li₂CO₃ can be leached out with water, leaving all other components, e.g., compounds of Cu, Mn and Al, for further recycling. Since the proposed process does not use or produce toxic substances, runs at relatively low temperature, yields high recovery for both Co and Li and can be run with simple equipment, it may be considered as suitable for immediate scaling-up and industrial implementation.

Electronic waste (e-waste) is a global concern, adding millions of tons of refuse that frequently contains environmental and biological toxins to landfills on a yearly basis. Efforts to extend the life of electronics through right to repair advocacy have thus far not been successful to curb the accumulation of e-waste. Recyclable electronics offers a promising solution to prevent this environmental disaster; however, demonstrations to date often evince recyclability or environmental compatibility through simple, single component demonstrations that focus on re-capturing conductive components. While these reports make pivotal progress towards green electronics, further investigations are required to create a truly revolutionary technology to thoroughly address the e-waste concerns—namely the accumulation of all components of an electronic device. Hence, a completely recyclable electrical device is desperately needed.

Through the use of nanocellulose as a dielectric, we report the creation of the first fully recyclable transistor device with a paper substrate, conductive graphene contacts, and a semiconducting carbon nanotubes channel. To further address environmental concerns associated with energy usage during device manufacturing, these electrical devices are printed almost entirely in a “print-in-place” fabrication procedure at room temperature with only a single toluene rinse at 80 °C. With the addition of a small concentration of table salt to the nanocellulose dielectric ink, these transistors have among the highest area specific on-currents and lowest subthreshold swings of any printed transistor (regardless of substrate) and maintain their performance over 6 months storage in air. Finally, after these devices complete their utility, they can be controllably broken down to their base components and the environmentally damaging nanomaterial inks (graphene and carbon nanotubes) can be recaptured for the later printing of new recyclable transistors with similar performance. The realization of fully recyclable electronics on a broad scale has the potential to be the watershed forestalling the environmental disaster that will inevitably result from the continued accumulation of electronic waste.

The combination of semiconductor technologies with micro-electro-mechanical systems (MEMS) as sensors and actuators has been developed in recent years. This technology combines a silicon wafer and a multilayer low-temperature cofired ceramic (LTCC) carrier and is named SiCer. Several design concepts were established and this innovative substrate technology is gaining importance in sensor integration (Stehr et al. 2019). The elaborated LTCC is adopted to the thermal properties of the silicon wafer and the bonding at the silicon-LTCC interface is the key to the versatility and robustness of the SiCer technology. This contribution focuses on the investigation of the microstructure transition at the bonding interface between silicon and LTCC. High resolution transmission electron microscopy investigations including a highly sensitive EDS for elemental analysis reveals phase transformations that take place during the combined bonding and sintering process of SiCer substrates. The observed phase evolution is discussed by means of thermodynamic considerations and conclusions on the bonding mechanism are proposed. The influence of the initial wafer surface including oxidic thin films is interpreted with regard to desirable SiCer substrate properties.

Stehr et al. 2019:
Stehr, Uwe; Hagelauer, Amelie; Hein, Matthias A. (2019): SiCer: Meeting the Challenges of Tomorrow's Complex Electronic Systems [From the Guest Editors' Desk]. In: IEEE Microwave 20 (10), S. 26–92. DOI: 10.1109/MMM.2019.2928614.

Multiferroic materials have the potential for many applications such as actuators, sensors, or memory devices, thanks to their magnetoelectric effect (ME). Such effect was first observed in inorganic single crystals but due to their low Curie temperature and their weak ME coupling coefficient, they were seldom integrated into devices. To overcome these limitations, the composite material strategy offers the opportunity to tune the ferromagnetic and ferroelectric properties of the two phases acting on the hybrid interface. In this context, we developed new flexible multiferroic composite materials through (i) smart tailoring of the hybrid interface between a ferroelectric and piezoelectric fluoropolymer, PVDF, crystallized in its β-polymorph to present suitable properties, and inorganic ferrimagnetic and magnetostrictive nanoparticles (NPs), cobalt ferrite (CoFe₂O₄), and (ii) effective control of NPs size [1] and surface chemistry [2].

To the best of our knowledge, up to now, there is no paper dealing with the sustainable preparation of hybrid CoFe₂O₄-PVDF films for magnetoelectric applications: Dimethylformamide (DMF) is still the most used solvent to prepare these materials since it is considered the best solvent to induce the crystallization of PVDF in its β-polymorph. However, it is now well-known that solvents with high polarity tend to induce the crystallization of β-PVDF [3]. Hence, the question raised is now: new solvents are doubtless required to improve the sustainability of the synthesis of PVDF-based films but will they be as efficient as DMF to induce the crystallization of β-PVDF in presence of 13 nm CoFe₂O₄ nanoparticles?
We present here our first studies on the synthesis of CoFe₂O₄-PVDF magnetoelectric thin films using less toxic solvents and their resulting properties. A comparison with the first series prepared in DMF is presented too.

[1] M. Bibani, R. Breitwieser, A. Aubert, V. Loyau, S. Mercone, S. Ammar, F. Mammeri, Beilstein J Nanotechnol. 10, 1166 (2019).
[2] C. Ben Osman, E. Barthas, P. Decorse, F. Mammeri, Colloids Surface A, 577, 405 (2019).
[3] F. Mammeri, Frontiers of Nanoscience 14, 67 (2019).

As product complexity in electronics increases, our consideration of the manufacturing, end of life processes and materials supply chains required to produce these electronics must keep apace of that complexity. Metrics that only cover technical performance miss opportunities to drive towards more sustainable approaches to design and processing. This presentation will discuss work in understanding materials availability and the potential for materials recovery to improve the sustainability of electronics. We will also describe materials market modeling work to understand limits on metals recycling policy to reduce primary mining for copper and other electronics-prevalent materials.

Nano-grained metal oxides can significantly improve the physical and chemical properties of the metal oxides for diverse applications that utilize a large surface area, such as gas sensors and catalysts. However, the inherent thermal instability of nanoscale grains is a major challenge and hinders technological applications that are operated at elevated temperatures. Thus, controlling the temperature-stability of nano-grained structures represents both a scientifically interesting problem as well as a major technological advancement to enable widespread applications of metal oxides.
Here, we report highly effective grain growth suppression in metal oxide nanoribbons to demonstrate the high-temperature stability of nanoscale grains. By controlling the metal to oxygen ratio and the nanoscale dimension of the initial amorphous metal oxide nanoribbons, we show that the average grain size was maintained at ~ 6 nm, despite high annealing temperatures up to 900°C for 6 hours. We find that excess oxygen in the initial amorphous metal oxide nanoribbons prevents the merging of small grains during crystallization, leading to suppressed growth of the small grains. This was verified by in situ transmission electron microscopy experiments, during which we directly observed crystallization of the nanoribbons. As an exemplary application that exploits nanoscale grains, we demonstrate a gas sensor using grain growth suppressed tin oxide nanoribbons, which exhibited both high sensitivity and unusual long-term operation stability due to the thermodynamically stable nanoscale grains. Our findings provide a new pathway to simultaneously achieve high performance and excellent thermal stability in nano-grained metal oxides, which will be useful for various device applications.

Bioresorbable electronics, which decomposed in the physiological environment after a designed period of stable function and corresponding byproducts are resorbed and vanish, have gained increasing interests in state-of-the-art biomedical implants for pre-diagnosis, monitoring and treatment of diseases, drug delivery which only requires the function for a certain period of time. Compared to other transient power supplies, such as piezoelectric nanogenerators, supercapacitors, bioresorbable batteries are promising power source with higher energy density and continuous output which typically are composed of bioresorbable material that degrade into non-toxic contents in physiological environment during and/or after discharge. State-of-the-art bioresorbable batteries are built upon Mg or Zn metal-based galvanic cells due to their good biosafety and electrochemical activity. Due to extreme high chemical activity of Mg, current Mg-based bioresorbable batteries all exhibited fluctuating voltage output and rapid output drops without a controllable lifetime, which cannot meet the requirements of an implantable power supply. Additionally, the fast degradation rate could induce localized releasing of concentrated hydroxyl ions, leading to inflammation or other harmful effects. Compared to Mg, Zn metal has moderate degradation rate which can circumvent undesirable local pH increase and minimize gaseous hydrogen evolution. Furthermore, in bioresorbable metal-based galvanic cell systems, although both the anode and cathode are needed, it is the metal anode that dissolves in the electrolyte and primarily determines battery lifetime and power output. Nevertheless, almost all current models were built on bulky foils or plates, where their degradation occurred naturally on the metal surface. Therefore, there was no control over the degradation rate, direction and sequence, and thus all showed a poor controllability on the battery output and lifetime, which further limits their practical applications. In this work, we report a bioresorbable zinc primary battery anode filament built on Zn micro-particles (MPs) coated with chitosan and Al₂O₃ nano-films. This battery filament exhibited a well-controlled dissolution direction and rate due to the mesoscale MP assembly, and the protective coatings. When discharged in 0.9% NaCl saline, single Zn MP filament with a 0.17 x 2 mm cross-section exhibited a stable voltage output of 0.55 V at a current of 0.01 mA, where the current and voltage output could be simply designed by integration of the battery filaments in parallel or in series, respectively. The operational time could be directly adjusted by the length of filament. A stable 200-hour discharging time was achieved by a 15 mm Zn MP filament. By increasing the filament cross-sectional area, higher current output can be achieved at the same discharging voltage, raising the output power. The final discharging byproducts, mostly ZnO/Zn(OH)₂ , could slowly dissolve in biofluids, making this composite filament completely degradable. This complete bioresorbable primary battery showed a full level of control of output and lifetime, providing a promising solution to in vivo powering transient bioelectronics.

The carbonization process generally is the conversion, by progressive heating, of organic molecular system to a macro network of carbon atoms. Network of porosity is produced as small molecules, such as water, methanol and carbon dioxide, are eliminated from the organic system and movement of atoms over short atomic distances create an intermediate stable phase of higher carbon content. Laser-carbonization provides a possibility of patterning which enable new potential applications for carbons for example micro charge-storage devices or electrical chemo sensors. The most famous precursors GO and PI are reduced to 3D-graphene to offer enormous activity as electrode materials due to high surface areas and high electrical conductivity. Carbon network-forming agents (CNFA) are formed by carbonization in the laser beam of carbon nanodots, produced from Urea and Citric acid under hydrothermal condition in microwave reactor. Annealing of the produced CNDs at 300^oC increases carbon content and form small graphitic domains. Finally, graphene is produced after laser induced reduction of carbon nanodots which is analyzed by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD). On the other hand, GO, a 2D nanomaterials with sp² hybridized thick sheet bears abundant oxygen-containing groups, such as hydroxyl and epoxy groups on the basal planes of GO and carboxyl groups at the edges of GO. Carbon nanotubes (CNTs) with one dimensional (1D) structure, possess excellent mechanical strength, extraordinary heat transfer capability and electrical conductivity. These properties make them promising materials for wide range of applications in nanotechnology. However, due to strong Van der Waals force applications in CNTs causes hydrophobicity and chemical inertness. They usually entangle with each other, as a result difficult for dispersion which limits their commercial applications. To solve this technical problem, the CNTs are tailored with surface modifications using chemical reactions. Various acid treatments are introduced to modify the CNTs surface structure, mild oxidation with acids yielded higher concentrations of carbonyl and hydroxyl functional groups while more aggressive oxidation form higher fractional concentration of carboxyl groups. These kind of approach are based on CH–π, hydrogen bonding or electrostatic interaction to adsorb functional groups on CNTs surface without any impairment of the original tube structure of CNTs. Thus, GO can be used with functionalized CNT to construct 3D GO/CNT hybrids through π-stacking interaction formed between the π-conjugated multiple aromatic regions of GO sheets and walls of CNTs. There may present another interaction in between the functional groups present in GO with oxygenated surface groups of modified CNTs. Due to this synergistic effect, this composite become an improved material for laser treatment. In this study, the electrochemistry of this hybrid structure is investigated as electrodes in bend form. R-GO/CNTs composite is initially characterize with FTIR and Raman spectroscopy and significant shifting in peaks with peak ratio from precursors indicates the presence of the composite further supported by XRD and XPS analysis. SEM and STEM were performed to investigate the dispersion and morphology of the composite. Thermal stability of functionalized CNTs is also an important issue for high temperature applications. Although, it is found that the acid treatment introduced carboxyl, carbonyl and phenol groups on the CNT surface, and ether-type oxygen between the two adjacent graphite layers, which decreased the thermal stability but it is shown to increase thermal stability of R-GO/CNTs composite. This hybrid material is useful as EDLC in terms of capacitance and improved stability make this composite a better material for the future applications.

Molecular spintronics is gaining attraction because molecules possess weak scattering mechanism. As a result, molecules retain spin information over a long time. Molecular Spintronics devices (MSD) are also considered crucial for futuristic quantum computing technology [1]. The major challenge of MSD is making robust and mass-producible spintronic devices at the nanoscale. To overcome this issue, we have designed a magnetic tunnel junction-based molecular spintronics device (MTJMSD). MTJMSD is fabricated by bridging paramagnetic molecules across the edges of the ferromagnetic electrodes. These molecules form dominant conducting channels over tunneling conduction between two ferromagnetic electrodes of an MTJ. MTJMSD enables the utilization of ferromagnetic electrodes with a wide range of magnetic anisotropies. Here, we are analyzing the magnetic switching mechanism, hysteresis loop (M-H Curve), and the overall magnetic properties of MTJMD as a function of anisotropies along with constant Heisenberg couplings.
In this paper, we report a theoretical Monte Carlo Simulation (MCS) study to explain the impact of anisotropies on the MTJMSD equilibrium properties. We also investigate theoretically how the nature of magnetic hysteresis changes as we apply the in-plane, out-of-plane, and in-plane and out-of-plane at the same time on the same ferromagnetic electrode. The application of anisotropy creates multiple magnetic phases of opposite magnetic spins on the same ferromagnetic electrode. When in-plane and out-of-plane anisotropies are applied on an electrode simultaneously, the magnetic moment of the electrodes possessed its maximum value. The MTJMSD possessed its maximum value since the competing effect of anisotropies wiped out the multiple magnetic phases.
In this study, we also investigated the effect of anisotropies on the nature of the hysteresis curves generated computationally using MCS. We applied the in-plane and out-of-plane magnetic anisotropies on the same ferromagnetic electrode of an MTJ. The effect of the in-plane anisotropy transformed the regular magnetic hysteresis of MTJMSD into a “wasp-waisted” -like hysteresis curve[2]. The “wasp-waisted” -like hysteresis curve is hypothesized due to the presence of multiple magnetic phases on the ferromagnetic electrodes caused by strong magnetic anisotropy. The application of equal magnitude of in-plane and out-of-plane anisotropies brings back the M-H curve into a regular hysteresis curve but with nearly zero coercivity. The zero coercive hysteresis closely agree with the experimentally measured M-H curves under the same situations. In this paper, we will also present the overall properties of MTJMSD when the spin fluctuations option is incorporated in the MCS code.


This research is supported by National Science Foundation-CREST Award (Contract # HRD- 1914751), Department of Energy/ National Nuclear Security Agency (DE-FOA-0003945).

References
[1] A. R. Rocha, V. M. García-suárez, S. W. Bailey, C. J. Lambert, J. Ferrer, and S. Sanvito, "Towards molecular spintronics," Nature Materials, vol. 4, no. 4, pp. 335-339, 2005/04/01 2005, doi: 10.1038/nmat1349.
[2] T. M. de Lima Alves et al., "Wasp-waisted behavior in magnetic hysteresis curves of CoFe 2 O 4 nanopowder at a low temperature: Experimental evidence and theoretical approach," RSC advances, vol. 7, no. 36, pp. 22187-22196, 2017.

Molecular spintronics is an emerging field that takes advantage of both spin properties and molecular electronics. The conjugation of spin degrees of freedom with molecular magnetic properties results in novel electronic devices with several advantages. The spin carriers carry and encode information in their spin state which allows development of efficient memory and logic devices [1]. Molecules have also unlimited passive and active magnetic properties that can be tailored with spin properties of atoms. Combination of spintronics with molecular electronics is an attractive method of making nanoscale devices with improved performance and functionality. Using organic molecules as conducting bridges between ferromagnetic electrodes has been a fascinating way of manipulating spin properties. However, the conventional techniques struggle with various challenges such as mass-producibility, endurability, and reliability of fabricated devices. In this work, we have proposed, and simulated a cross-junction shaped spintronic device called magnetic tunnel junction based molecular spintronic device (MTJMSD) using Monte Carlo Simulation (MCS) to investigate spin-dependent charge transport phenomenon. MTJMSD is made of two ferromagnetic electrodes (FME) separated by a few nanometer-thick tunneling barrier. Unlike previous methods, magnetic molecules are attached on the exposed edges of the FM electrodes in the outer world [2-4].
The interaction between magnetic molecules and FM electrodes, strengths and nature of couplings, molecules and electrodes’ type, thermal energy, and several other factors play important role in defining MTJMSD ultimate properties. In this work, we have computationally investigated few parameters (e.g., Heisenberg exchange coupling, electrodes’ size, thermal energy, spin fluctuation) that affect MTJMSD’s magnetic properties. Our results show that the magnetic couplings between molecules and FM-electrodes have a dominant role in dictating MTJMSD’s magnetic moment and spin orientation. Antiferromagnetic and ferromagnetic molecule-FME couplings forced the FM electrodes to take antiparallel and parallel spin states with respect to each other respectively at room temperature. Our results also showed that despite significant increase in time evolution of magnetic moment, stability is not achieved at higher temperatures. The electrodes’ size (length and thickness) affected molecules’ ability to induce magnetic properties in FM electrodes to some extent. However, the nature of coupling between FMEs is still dictated by molecules at stronger Heisenberg exchange coupling values. Spin fluctuation increased equilibrium energy and temporal evolution of magnetic moment compared to the non-spin fluctuation case. It also introduced some stripe-shaped spin orientation within electrodes. The current MCS studies complement our ongoing experimental research which investigates the effect of organometallic molecules on MTJ’s hysteresis loop and saturated magnetic moments.
Acknowledgement:
This work is supported by National Science Foundation-CREST Award (Contract # HRD- 1914751), Department of Energy/ National Nuclear Security Agency (DE-FOA-0003945).
References:
1. A. R. Rocha, V. M. García-suárez, S. W. Bailey, C. J. Lambert, J. Ferrer, and S. Sanvito, "Towards molecular spintronics," Nature Materials, vol. 4, no. 4, pp. 335-339, 2005/04/01 2005, doi: 10.1038/nmat1349
2. P. Tyagi, C. Baker and C. D'Angelo, Nanotechnology 26, 305602 (2015).
3. P. Tyagi and E. Friebe, J. Mag. Mag. Mat. 453, 186-192 (2018).
4. P. Tyagi and C. Riso, Organic Electronics 75, 105421 (2019).

ZnO has been highlighted as one of the most attractive candidates for water splitting due to its high oxidation power, chemical stability, non-toxicity, and low production cost. Despite its superior intrinsic properties, there exist a few reports on photoelectrochemical (PEC) water splitting with pure and monolithic ZnO. Due to the large energy band gap (3.2 eV) ZnO can be activated only under the ultra-violet light irradiation, which seriously limits its broad applications to water splitting. Thus, to overcome this drawback most researches on PEC water splitting with ZnO have been focused on the impurity doping for energy band gap modification, the noble metal decoration for the plasmon resonance energy transfer (PRET), and the type II heterojunction formation with other semiconductors for visible light absorption.
Here, we report the breakthrough for the water splitting of pure ZnO photoelectrodes. First, we developed the growth method of high-density and faceted ZnO micro-rod (MR) structures on a conductive substrate. Subsequently, nano-branches were grown all over the facets of ZnO MRs using a dip coating followed by hydrothermal synthesis to realize ZnO nanobrush (NB) structures. The ZnO NB electrodes (NBEs) revealed the photocurrent density of 1.687 mA/cm² at 1.23 V_RHE and 0.48% conversion efficiency (ABPE) at 0.81 V_RHE, which is as far as we know the highest conversion efficiency value among monolithic ZnO photoelectrodes. The length of nano-branches could be precisely controlled by the solvothermal reaction time. As-synthesized ZnO NBEs exhibited photocurrent density ~1.36 times higher than that of bare micro-rod electrodes (MREs). The role of nano-branches in the photocurrent density increase was verified by the open-circuit potential and Nyquist plot analyses. The extra space charge region (SCR) occurring by introducing nano-branches on the surfaces of ZnO MRs was for the first time proposed as a mechanism for the increased photocurrent density in the ZnO NB structures.

Separation processes are ubiquitously employed for purification purposes in chemical production, as well as potable water generation and environmental remediation. The rising intensity of global issues such as the growing world population, low water security, and worsening industrial pollution all necessitate further advancement in the discovery, development, and application of materials for separations. Electrochemical approaches are an attractive alternative due to the innate propensities of redox-active species for modular design, molecular recognition, reversible operation, and lower energetic requirements, all of which can be realized via only electrochemical stimuli without any chemical additives. The current state-of-the-art for sustainable electrochemical separation technologies was delineated in a recent review,¹ and include electrochemically-mediated techniques at its forefront. In this work, the focused design of redox-active materials for imparting specific functionalities to electrosorption processes are discussed.

Redox-active composite materials have been developed from four different classes of electroactive species in order to enable redox-mediated ion detection and removal in water, with designed controllability over their pseudocapacitance, stability, analyte selectivity, and energetics. Anion separation was achieved using an organometallic ferrocene co-polymer whose electrochemical activity in different electrolyte solutions can be manipulated based on its co-monomer.^2,3 Through principles of hydrophobicity, the metallopolymer can be engineered to activate in the presence of hydrophilic anions instead of hydrophobic ones, for subsequent application in the stable and seven-fold selective electrochemical extraction of perrhenate over nitrate. The ferrocene macromolecule motif was also extended to the generation of zwitterionic polyelectrolytes that possess pH-sensitive electrochemical behavior in both homogeneous and heterogeneous environments.⁴ Cation separation was facilitated through the preparation of pH-dependent quinone and electronically-tunable crystalline hexacyanoferrate-based conductive electrodes, which were paired together with polymeric ferrocenes to produce asymmetric redox-active systems that could reduce the extent of anode fouling by preventing parasitic water reduction, offer optimizable separation energies, allow for the enhanced and simultaneous recovery of transition metal compounds without altering their bulk oxidation state, and enable continuous operation under flow conditions.^2,3 Lastly, redox-active components were incorporated into a particulate scaffold instead of an electrode framework with the purpose of further improving their potential for ion separation through heightened maneuverability and phase contact provided in part by the judicious variation of material hydrophilicity.⁵ Polypyrrole and polyferrocene-containing magnetic composites were synthesized through a facile multi-step procedure, and exhibit strong adsorption capacities for both inorganic and organic contaminants.

References:
1. Tan, K-J.; Hatton, T.A., Sustainable Separation Engineering 2021, Accepted.
2. Tan, K-J.; Hatton, T.A. et al., Adv. Func. Mater. 2020, 30 (15), 1910363
3. Tan, K-J.; Hatton, T.A. et al., 2021, Submitted.
4. Tan, K-J.; Hatton, T.A. et al., 2021, In Preparation.
5. Tan, K-J.; Hatton, T.A. et al., 2021, In Preparation.

Kesterite-based Cu-Zn-Sn-S (CZTS) solar cells with layer stacking of Al/Al:ZnO/ZnO/CdS/CZTS/Mo are attracting attention in last few years, owing to less toxic and more abundant elements [1-2]. However, the current efficiency of CZTS champion solar cell is 11.01% that shows high disparity from its counterpart, Cu–In– Ga–Se (CIGS) solar cell [3]. High voltage deficit in CZTS solar cells is one of the primary cause of low efficiency. The lower performance of CZTS solar cells is mainly attributed to high open circuit voltage deficit due to increased interface recombination. Therefore, absorber-buffer interface engineering is essential and deserves more investigation to understand the charge dynamics at the interface. Here, we report wide band gap (3.8 eV) TiO₂ as a potential candidate to substitute conventional CdS buffer layer with low-band gap (2.4 eV) and toxic in nature. The surface and interface of CZTS-TiO₂ layer was investigated using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The result reveals favourable “spike”-like conformation at CZTS-TiO₂ interface with conduction band offset (CBO) value of 0.17 eV. The nanoscale probing of interface by Kelvin Probe Force Microscopy (KPFM) across CZTS-TiO₂ layers show a higher potential barrier for interface recombination at CZTS-TiO₂ in contrast to conventional CZTS-CdS interface. Finally, the fast decay response and lower persistent photoconductivity (PPC) of photogenerated carriers for CZTS-TiO₂ heterojunction based photodetector, further validate our results. Carrier management via interface engineering using emerging materials will help to obtain high efficiencies in CZTS solar cells.

The impact of double donor doping on the crystal structure, morphology, film compositions, emission and electrical properties has been studied in the ZnO:Ga:In nanocrystal films. The films were deposited by ultrasonic spray pyrolysis on silicon substrates heated to 400^oC. To the study of double donor doping, two groups of samples were prepared. In the first group the In content was of 1at%, but the Ga contents were varied in the range 0.5-3.0at.%. In the second group the In content was of 2at% and the Ga contents were changed in the range 0.5-2.5at%. To stimulate the film crystallization, all samples were annealed at 400 °C for 4h in a nitrogen flow (5L/min).
The variation non monotonous of the crystal lattice parameters, compositions, the PL intensities, and electrical resistivity has been detected in the ZnO nanocrystal (NC) films. The high-quality NC films with the wurtzite-type crystal structure, planar morphology, bright near band edge (NBE) emission and the small intensity of defect related PL bands have been obtained. The reasons for parameter varying non monotonically and the optimal concentrations for the Ga/In double donor doping of ZnO NC films have been analyzed and discussed.

We aim at providing functionalized encapsulation of Halide Perovskites (HaPs) to prevent Pb from reaching the environment, especially the groundwater, in case of module device damage/breakage and subsequent exposure to the elements. HaPs are widely explored in research and development, specifically for optoelectronic devices, including large-scale outdoors employment in solar cell panels, due to their outstanding properties as light-absorbing materials. The most efficient devices use a Pb-based HaP. PbI₂ and PbBr₂, together possibly with oxides/hydroxides, are the most likely decomposition products if devices are broken and the HaP is exposed to the ambient. As these Pb dihalides are soluble, albeit sparingly, in water, exposure to rain can release Pb ions that may reach the groundwater.
Such a scenario carries obvious environmental and public health risks. We show here how to mitigate and even eliminate this scenario by efficient sequestering of Pb ions. A scheme of ligands is presented for sequestration as part of an encapsulation, using commercial materials and methods, reaching, till now, 90% lead retention in a commercially viable process.

Energy-efficient devices based on renewable and economical sources are in high demand to meet the daily needs of people. Electrochromic devices are used to control light and heat to pass through the material when voltage is applied across it. They are widely used in smart windows or mirrors, smart sunglasses, sunroofs, anti-glare car rear-view mirrors, and to store optical information, are based on the phenomenon of electrochromism.
Electrochromism is a phenomenon that causes changes in the optical properties of the material due to the injections and extractions of the charge carriers/ions or redox reactions. Injections and extractions of charge carriers/ions persuade changes in the electronic distribution of the crystal network of the electrochromic material, affecting the optical property. The change in the colour of the material is termed as coloration and bleaching effect. Injections of charge carriers/ions result in coloration of the materials while extracting carries/ions causes bleaching effect. Materials that show electrochromic properties retain the capacity to change their colour as a response to an electrical impulse and thus makes that material flexible for the device application.
Commonly used materials in this phenomenon are transitions metal oxide-based materials like tungsten oxide, titanium oxide, nickel oxide, molybdenum oxide, etc. Recently, Nickel oxide (NiO) based electrochromic devices results as a promising electrochromic material as it allows absorptance modulation. NiO is a p-type, wide bandgap (3.6-4.0eV) semiconductor with better reversibility, fast coloration efficiency and high optical modulation material. In the current paper, NiO has been synthesized using the Hydrothermal technique and the peaks obtained in the XRD pattern validates NiO nanoparticles. FESEM images depict synthesized NiO nanoparticles are pyramid-shaped structures. Explanation of electrochromism phenomena using Cyclic voltammetry, Chronoamperometry and Electrical Impedance Spectroscopy will form the complete part of the paper.

Transparent conductors (TC) have great importance in day-to-day life and state of the art high-tech applications. For instance, they are used in light-emitting diodes, solar cells, transparent thin film resistors, display devices, and many others due to their good electrical conductivity and high transmittance in the visible region. However, current materials used for the TC are very costly. Current research interest is to develop low-cost TC with better electrical conductivity and high optical transmittance. The objective of this work is to tune the electrical and optical properties of low cost Al₂O₃/ZnO multilayer heterostructure on quartz substrates through anion as well as cation doping in ZnO and find out a better TC. All the heterostructures were made using pulsed laser deposition technique through varying growth parameters such as oxygen pressure, substrate temperature, and number of laser shots. The initial sample was a pristine ZnO layer, followed by a 95/5 ZnO/Al₂O₃ superlattice, then 90/10, and 80/20. To enhance electrical conductivity with minimum reduction in transmittance, the samples were annealed under forming gas (96% Ar and 4% H₂). The structure of the heterostructures was characterized via X-ray diffraction (XRD), Raman spectroscopy, photoluminescence (PL), and scanning electron microscopy. The electrical conductivity of the samples was determined via four probe electrical measurements, and the optical transmittance was determined by UV-VIS spectroscopy. XRD and Raman spectroscopy data confirm the presence of Al-doped ZnO and Al₂O₃ in the sample. The PL spectroscopy indicates the presence of oxygen as well as other point defects in the samples and specially, the number of oxygen vacancies increases with annealing. The optical measurements show that the transmittance of the superlattice oxide thin film decreases from 90 to 80 % with annealing. However, the electrical conductivity increases 4-6 order of magnitude with annealing. The resistivity decreases from 2 Ohm-cm to 6.2 E-03 Ohm-cm for the optimum sample. This multilayer heterostructure oxides can be useful for developing low-cost TC for optoelectronic applications.

The recent discovery of Q – carbon has opened ways for the fabrication of fascinating heterostructures using the non-equilibrium technique of nanosecond pulse laser annealing. Q- carbon is reportedly the densely packed metastable state phase of carbon with about 80% sp³ content. The pure Q- carbon exhibits extraordinary hall effect and room temperature ferromagnetism whereas the Boron doped Q- carbon shows superconductivity. In Q carbon films which we have grown on sapphire, we observed that these magnetic and electrical properties can be attributed to the abundant unpaired electrons near the fermi energy level. This talk will put a light on the ferromagnetic properties as a function of size. With the increase in the size, we observe that the ferromagnetism increases up to a critical size. It is very interesting to see how does the magnetism changes with the size and what is this critical size. This will be an interesting lead in the magnetic and electron transport properties of Q- carbon which will enhance the functionalities of the fabricated devices and its application in carbon based spintronics.

Recently, there is an increased demand for the development of multifunctional materials and hence they have allured enormous interest in every other application possible. With the threat of escalating electromagnetic (EM) pollution, there is a strong need to develop materials and strategies to curb it. Textiles have been used as promising candidates for electromagnetic waves, particularly in the microwave frequency ranges, owing to their numerous advantages like flexibility, lightweight and conformability. In addition, it is beneficial in creating multiple interfaces for microwave attenuation on textiles with functional coatings. Herein, we report for the first time, the preparation of a multifunctional coating that is based on iron titanate (FT) and multiwalled carbon nanotubes (CNT) which can shield both microwaves and UV radiations. The iron titanate used here is sourced from a sustainable precursor – the ilmenite sand, while the CNT is commercially sourced. In order to demonstrate the contribution of FT in EMI shielding, another particle was also used – this was synthesized in the same protocol as that of FT with copper ions incorporated (CuFT). On comparison, it was found that FT tends to interact with and attenuate EM radiation along with CNT – much better than CuFT. The coated fabrics show an EMI shielding effectiveness of -30 dB for a stack of four layers in the broadbands viz. X and Ku – translating to a 99.9% attenuation of the incident EM signals. Further, there is a jump in conductivity of around four orders in magnitude for the coated fabric in comparison to the neat fabric. It is worth to note that the coating confers an ability to block 99.9% of the UV radiation over the wavelength ranging 200-400 nm. Furthermore, the prepared coatings significantly improve the flame retarding properties of the neat fabric. With such remarkable properties, these coatings have the huge potential to significantly enhance the commercial value of cotton fabrics without adding much to its cost.

Anisotropic etching of silicon is usually performed using alkaline etchants such as aqueous KOH, TMAH and other hydroxides like NaOH. A large variety of silicon structures can be fabricated in a highly controllable and reproducible manner with the strong correlation of the etch rate due to the orientation of the crystal structure, etchant concentration and temperature. Therefore, anisotropic etching of <100> silicon has been a key process in common MEMS based technologies for realizing 3-D structures. These structures include V-grooves for transistors, small holes for ink jets and diaphragms for MEMS pressure sensors. The actual reaction mechanism has not been well understood and comprehensive physical and chemical models for the process have not yet been developed. With increasing numbers of MEMS applications, interest has grown in recent years for process modelling, simulation, and software tools useful for the prediction of etched surface profiles [1-4]. Utilizing near infrared spectrometry (NIR) technology allows TMAH/KOH concentration to be controlled effectively while monitoring the silicate concentration within the bath during the silicon etching process. This technique allows for higher uniformity and longer continuous etching times without interrupting the wafer process within the tank. While maintaining the Si concentration, the system will partially drain the tank bath mixture and replenish it with fresh chemical of each component at the desired concentration [5]. This was effective to a specific number of wafers to be processed in one lot batches, however with this new application the number of wafers processed per lot has been increased two-fold. In the present study, controlling the production of the H₂ byproduct from the etching reaction with TMAH/KOH while monitoring the bath concentration increases the overall throughput. The chemical solution travels through a new application which allows the hydrogen gas to be released from the solution and transferred to the top of the tank effectively removing from the solution. The now H₂ gas removed solution then re-enters the tank, with minimal H₂ in the solution, removing the chances of any contamination blocking the Si wafer and decreasing the uniformity or etching. The results show that the number of wafers per lot have been increased via controlled chemical replenishment while mitigating the hydrogen gas by-product. With this new application the process can run higher throughput, even with long etch processing times for Si.

1. K. Peterson: Silicon as a Mechanical Material (IEEE Proceedings, San Diego, CA, 1982).
2. Alvi, P.A., et al, Int. J. Chem. Sci., 6 (3), 1168-1176 (2008).
3. K. Sato et al., Sensors and Actuators, 64, 87-93 (1988).
4. M. Sekimura: Anisotropic Etching of Surfactant-Added TMAH Solution (12th IEEE Conference on MEMS Proceedings, Orlando, FL, 1999).
5. Kashkoush, I., Rieker, J., Chen, G., & Nemeth, D. (2014). Process Control Challenges of Wet Etching Large MEMS Si Cavities. Solid State Phenomena, 219, 73–77. https://doi.org/10.4028/www.scientific.net/ssp.219.73

Energy efficient computing and memory-storage devices are key to further increases in high performance computing that is essential to today’s data centric world. We discuss, on the one hand, Magnetic Racetrack Memory[1, 2] that promises a high capacity, high performance, non-volatile, memory-storage device that could supplant magnetic disk drives and solid-state FLASH, and, on the other hand an extremely energy-efficient memcapacitor device[3] that could allow for massive neuromorphic computing systems.

1 Yang, S.-H., Naaman, R., Paltiel, Y., and Parkin, S.S.P.: ‘Chiral spintronics’, Nat. Rev. Phys., 2021, 3, pp. 328–343
2 Bläsing, R., Khan, A.A., Filippou, P.C., Garg, C., Hameed, F., Castrillon, J., and Parkin, S.S.P.: ‘Magnetic Racetrack Memory: From Physics to the Cusp of Applications within a Decade’, Proc. IEEE, 2020, 108, pp. 1303-1321
3 Demasius, K.-U., Kirschen, A., and Parkin, S.: ‘Energy-Efficient Memcapacitor Devices for Neuromorphic Computing’, Nat. Electron., 2021, accepted

The future in functional materials manufacturing has to have the challenge of resource criticality in mind. Ways to address this issue include providing resource efficient material manufacturing methods (e.g. additive manufacturing of functional materials) and reducing the use of critical materials by providing alternative materials or resources such as efficient recycling processes. While additive manufacturing has advantages to more energy demanding and waste producing methods, this method has to be adjusted for the use of sustainable printing materials and the production of functional materials for sustainable technologies such as green ICT. This would reduce not only the energy demand of ICT systems, but also increase their materials sustainability.
Our activities on recyclate-based additive manufacturing is based on materials flow analysis and electronic waste recycling. The goal is a versatile process for recyclate powder production to provide sustainable printing materials for additive manufacturing of functional materials in high-tech technologies. We present our plan for the close connection of efficient recycling and powder production techniques, our technical capability at Fraunhofer IWKS and give an overview of the research questions we are working on.

Researchers have been using different approaches to address challenges in the fabrication of sustainable building materials such as reproducibility, reliability, and using renewable materials while preserving properties. Despite these efforts, there are still fundamental limitations in the current fabrication methods of such materials. To solve those challenges, investigators have been studying recently wood-based insulating material, in combination with ceramic binding agents, to create novel green materials for housing applications. This new material can lead to fully capable load-bearing house components (e.g. wall systems) with high-insulation high-strength properties, where burning is not required in the molding process of the sample preparation. In this study, we have investigated the properties and ecological traits of the new green material by calculating composition-dependent properties and life-cycle assessment (LCA) via physics-based modeling. Using eco-audit data and materials design software, we have conducted systematic analyses of several housing siding samples and evaluated traits including mechanical properties, price, energy, and CO₂ footprint. We evaluated the role of material composition, binder type, and the environmental impact of potential house sidings made of cedarwood, fiber cement, pine-magnesia, and flame block-oriented strand board (OSB). Results indicate the most impactful material for house sidings is Flame block OSB. The effect of resins (painting, enamel baked coating, polymer powder coating) was also evaluated and LCA results show that OSB with polymer powder coating is the least eco-friendly in the manufacturing stage. The hypothesis is that by modifying the siding’s composition and binder type, the impact on the environment could be further decreased. Overall results from this study were found to be in good agreement with recent experiments reported elsewhere independently, and mechanical properties together with LCA data of the new green material are significant in determining sustainable alternatives compared to other counterparts. This research contributes to improving material discovery by the combination of design, predictive modeling, and LCA evaluation which allows researchers to determine the technical and commercial feasibility of new sustainable house components.

With the rapid development of transparent integrated circuits, the requirement of transistors with lower subthreshold swing (SS) is becoming necessary. Here, we fabricate three device structures showing abrupt switching and make their series connection with conventional field effect transistors (FET) to lower the SS value. Firstly, we demonstrate an environmentally friendly, disposable, and transparent conductive bridge random access memory (CBRAM) device, composed of 99.3 vol.% nanocellulose fiber. Our CBRAM consists of silver (Ag) electrochemically active electrode and nanocellulose fiber (ca. 15 nm) based switching layer on FTO coated glass substrates. Devices with CBRAM can enable the FET with lowest SS slope by switching the metallic filament between ON and OFF. Niobium oxide (NbO₂) based threshold switching devices and zinc oxide (ZnO) based transparent and flexible Schottky diodes with electrical breakdown were also stacked with FET giving the SS < 10 mV/dec. Comparatively, the transistor plus CBRAM stack can significantly improve the SS slope with lowest leakage current compared to the other series stack, showing the great potential to boost the development of the future generation workhorse transistors.

The stability of polar oxide surfaces has long been an interesting topic in surface science. Since the electrostatic potential diverges with increasing polar oxide thickness, various screening processes involve such as surface reconstruction, charge transfer, and adsorption of foreign charged species. Here, combining the density functional theory calculations and molecular dynamic simulations, we report that the vicinal surface steps can completely stabilize the polar oxide surface without introducing defects and excess charge. The evolution of steps at the vicinal surface, and resulting stabilized polar surface will be discussed and associated underlying mechanism will be introduced along with atomic-scale scanning transmission electron microscopy images.

Organic photodiodes (OPDs) are expected to play an important role in the development of sustainable electronics since they can be used for photovoltaic or photodetector applications and be fabricated in biodegradable susbtrates, such as those based on nanocellulosic materials, and be easily recycled [1]. To optimize the properties of organic semiconductors used in such devices for photodetector applications, it is critical to develop an improved understanding of the electronic noise characteristics of OPDs. In the dark, the electronic noise current of a photodetector such as an OPD determines the lowest detectable optical power [2]. Yet the physical origin of the electronic noise current and its relationship with the dark current measured in steady state is rarely studied through direct measurements and consequently remains poorly understood [2,3,4].
Using detailed temperature- and optical power-dependent studies of the electrical characteristics of OPDs, we demonstrate that grounded in thermodynamic principles, the steady-state optoelectronic properties of OPDs can be described using an equivalent circuit approach to derive the reverse saturation current, ideality factor and shunt resistance values as a function of temperature.
These detailed studies reveal that the reverse saturation current is thermally activated with a barrier height that is equal to the transport bandgap divided by the ideality factor. The value of the ideality factor is well-approximated as the inverse of the recombination order of the limiting recombination process in the dark, yielding a value between 1 and 2 for most common recombination mechanisms, such as band-to-band recombination and trap-assisted recombination, either through mid-gap states or through an exponential trap distribution (Urbach tail).
Derivation of these parameters and its thermal dependence enables an accurate description of the current density in OPDs in the dark as a function of voltage and temperature and under illumination conditions varying over nine orders of magnitude. Furthermore, thermodynamically consistent expressions for the shot and thermal noise contributions using the reverse saturation current and shunt resistance values derived experimentally, are used to estimate the white noise electronic noise current. This analysis shows that at the low measurement bandwidth values typically used to characterize OPDs, the electronic noise is limited by flicker noise even in OPDs showing electronic noise current values in the tens of femtoampere. Critically, we show that the electronic noise at low measurement bandwidth values does not scale with the steady-state dark current density, as it is often assumed in the literature.
These findings, have important implications for the accurate characterization of OPDs, but also, reveal the critical role that trap-assisted charge recombination and the width of the transport bandwidth play in determining their steady-state dark current characteristics. Although these material properties play a critical role in determining the magnitude of the white noise, our results suggest that they may play a secondary role in determining the magnitude of the electronic noise in OPDs at low measurement bandwidth values.
[1] Y. Zhou, et al. Sci Rep 3, 1536 (2013).
[2] C. Fuentes-Hernandez, et al., Science, 370, 698 (2020).
[3] Y. Fang, et al., Nature Photonics, 13,1 (2019).
[4] J., Kublitski, et al. Nat Commun 12, 551 (2021).

The formation of a passivating and selective back contact is necessary for constructing CdTe solar cells with an open circuit voltage greater than 1 volt. Recombination at the back surface and a large back-contact barrier are widely recognized as major problems limiting CdTe solar-cell performance. Other solar cell technologies have demonstrated the use of metal oxides to help passivate the back contact. We explore the use of tellurium oxide as a passivating buffer layer to improve device performance. In these experiments we study the effect tellurium oxide’s () thickness, treatment, and process gas composition have on device performance. The large bandgap of also has implications for electron reflectors, to reduce recombination at the surface, and bifacial applications. The effects of on device performance are characterized by current-voltage and quantum-efficiency measurements, showing efficiencies and open-circuit voltages up to 17.5% and 849 mV. Admittance and capacitance voltage measurements are used to study the depletion width and carrier concentration, while time resolved photoluminescence measurements are used to explore the effects on recombination. We found cells with carrier densities up to 1e15 carriers per cubic centimeter and carrier lifetimes up to 160 ns. Our results demonstrate the viability of as a buffer layer to improve passivation and performance in CdTe solar cells. An added benefit of is the ability to utilize an undoped absorber, which is crucial to reduce degradation in CdTe solar cells.

Supercapacitors have attracted tremendous interests due to their long-term stability and high power density derived from fast charge/discharge rate. Among them, heteroatom-doped porous carbon materials have been extensively explored and synthesized for industrial applications. However, their complex and time-consuming synthesis routes impede scalable fabrication. Herein, we report a facile one-pot synthesis strategy of nitrogen-doped hierarchical porous carbon void shell (N-HPCVS) using combustion waves. Free-standing films were prepared by mixing recrystallized sodium chloride particles with collodion, which is a nitrocellulose solution, where the particles and the nitrocellulose could act as templates and fuel covering the precursors, respectively. When a heat source, enabled by a joule-heated nichrome wire applied to the film, the combustion wave appeared as an instant thermochemical processing and propagated along the whole film within ten seconds. Owing to the rapid combustion waves involving the functional reaction of the NaCl particles, which could manipulate the thermodynamic transition, the incomplete combustion naturally occurred, and the carbon residue around the templates remained as resulting materials. Since the nitrocellulose comprises cellulose with nitro-group, the remaining carbon spontaneously includes nitrogen dopants. Through simple rinsing with DI water, the NaCl templates were removed and N-HPCVS were finally obtained. Owing to the thermal decomposition of NaCl templates and sudden evaporation of gases during the propagation of combustion waves, the hierarchical porous structure of N-HPVCS comprising of macro and meso-/micro-pores was completed.. Furthermore, the tunable physicochemical characteristics of N-HPVCS could be achieved by only optimizing initial fuel loading. Based on screening the processing conditions of combustion waves, the properly adjusted N-HPCVS30 which was prepared with 500 mg of NaCl and 30 g of collodion, exhibited outstanding specific capacitance (305 F/g at 0.5 A/g) and long-term cycling stability (116% retained after 10,000 cycles). Furthermore, the symmetric two-electrode cell employing the N-HPVCS presented remarkable power and energy density (25 kW/kg and 18.8 Wh/kg), as well as long-term cycling retention (98.25 % after 10,000 cycles). The rational fabrication strategy of N-doped hierarchical porous carbon using the combustion waves will inspire fascinating hybrid electrodes and catalysts which cannot be achieved through conventional synthesis methods.

Reconciling results from conventional and hybrid density functional theory is important to establish the level of accuracy achievable and best practices in first-principles simulations of defects in semiconductors. We present a case study to assess the extent to which calculations performed with (i) Perdew, Burke, and Ernzerhof (PBE) combined with systematic band edge shifts and (ii) Heyd, Scuseria, and Ernzerhof hybrid HSE06 can reproduce experimental results for gold-related defects in silicon. Substitutional Au_{Si}, substitutional dimers Au_{Si}--Au_{Si}, and tetrahedral interstitials Au_i are considered in detail.

In this manuscript, we report a recent investigation of the structural, electronic and optical properties of the new quaternary chalcogenide Cu₂NiSnSe₄ (CNTSe). Our calculations were done using the first principle approach. We have employed the full-potential linearized augmented plan-wave (FP-LAPW) method implemented in wien2k code. To treat the exchange and correlation effect of our numerical calculations we used the Tran-Blaha modified Becke-Johnson potential combined
with the Hubbard potential U (mBJ+U). Our numerical calculations showed that CNTSe exhibit high absorption and direct bandgap. We also determined the real and imaginary parts of the dielectric function, the reflectivity, and the refraction index.

Lignin, which is contained in woody biomass at 20 to 30%, is a polymer with a three-dimensional network structure in which complex aromatic molecules are bonded. It was abandoned. If useful applications can be established by converting lignin into high value-added organic materials, it can be expected to greatly contribute to the formation of a recycling society. In 2006, a technology for producing 2-pyrone-4,6-dicarboxylic acid (PDC), which is an intermediate metabolite of lignin, was developed using the lignin metabolism system of the bacterial SYK-6. Focusing on the high electron acceptability of PDCs, we have developed various charge transfer salts based on PDCs and investigated their structures and electrical properties. Therefore, we have focused on tetrathiafulvalene(TTF) derivatives as electron donors, and have synthesized charge-transfer salts with PDC using these molecules by electrolytic method and clarified their various physical properties.
In this study, we expanded our research to asymmetric electron donors with the TTF molecular framework. we have synthesized the several kinds of charge-transfer salts with asymmetric TTF derivatives by taking advantage of the low crystallinity based on the asymmetry.
In this study, we report the results of systematic investigation of these crystal morphologies, crystal structures, electronic properties and magnetic properties, as well as the differences in structure and properties of charge-transfer salts with symmetric TTF derivatives.

The current transformation in the mobility sector is accompanied by a change in the materials needed for the new key components. Rechargeable batteries are one imperative in electro mobility. The same holds for their usage in mobile devices, power tools and stationary energy storage devices. Equally important for electro mobility, but also for the other named devices, are the high performance permanent magnets, which are used in motors with the highest efficiency, lowest weight and volume. Every battery in a modern electric vehicle needs a magnet; the more efficient the magnet the less battery is needed, the longer the driving range. Batteries as well as motors contain valuable and resource critical metals elements such as neodymium, dysprosium, cobalt, lithium, and copper. The mining of these elements is intense in energy and chemical consumption. Furthermore, they also contain substances that would endanger our environment and health if disposed of improperly. Effective recycling of end-of life products is therefore of great relevance from both an economic and an ecologic point of view. Using the technosphere will also yield some leverage from the monopolistic supply situation for primary strategic metals.

We will highlight first in this talk the Center for Dismantling and Recycling for Electromobility, which is build up at Fraunhofer IWKS in Hanau. Here, the robot assisted dismantling and recycling of key components of electric vehicles like batteries, fuel cells, electric motors and power electronics are in the focus. For traction motors in electric vehicles, permanent magnets based on rare earth elements (REE) like Nd-Fe-B and Sm-Co are used due to their outstanding magnetic performance in a wide temperature range. The global demand for REE will increase drastically in the near future. To meet this demand and to secure the supply for other magnet applications several recycling techniques for permanent magnets are highlighted. The recycled magnets show a low environmental footprint and compete well with those made from primary materials in terms of magnetic properties and cost.

In a second part, we will focus on secondary properties of permanent magnets. The driving force for R&D has been the demand for superior primary magnetic properties. Now, the increasing number of applications using Nd-Fe-B permanent magnets in more severe conditions leads to extended requirements for the magnets. In fly wheel energy storages or electric motors for example, high rotational speeds are used. The resulting high forces on the magnets and can lead to a magnet failure due to the high intrinsic brittleness of Nd-Fe-B intermetallic compound. Concepts for Nd-Fe-B based magnets with high fracture strength are introduced.

Based on a definition of the MacArthur Foundation a circular economy is “Looking beyond the current take-make-waste extractive industrial model, a circular economy aims to redefine growth, focusing on positive society-wide benefits. It entails gradually decoupling economic activity from the consumption of finite resources, and designing waste out of the system. Underpinned by a transition to renewable energy sources, the circular model builds economic, natural, and social capital. It is based on three principles:
Design out waste and pollution
Keep products and materials in use
Regenerate natural systems”
NREL has initated a comprehensive program to examine a number of supply chains from raw materials to end of life and recycling. Key observations are that you can design even complicated systems to have nearly zero environmental impact and lead to true sustainability. An important element of this is to develop materials systems that are not only reusable but are also self healing and self restoring. A true circular economy incorporated te concepts of increased use of renewable electrons for many processes and improved approaches to grid and storage utilization.
We will discuss practical examples of this approach including: approaches to solar energy conversion with earth abundant non-toxic elements, lifecycle extension of materials in PV, Wind, and energy storage. A key element of a long term strategy can be illustrated in the polymer and composites area where materials are designed for easy end of life reuse and where self-healing materials can extent initial lifetimes substantially. This is especially true as we move to the “electrification of everything”. We will discuss new approaches to materials design for longevity, self healing and ultimate recycling where these approaches are ultimately enabling for a true circular economy.