Photocatalytic doping of organic semiconductors.

Chemical doping is an important approach to manipulating charge-carrier concentration and transport in organic semiconductors (OSCs)1-3 and ultimately enhances device performance4-7. However, conventional doping strategies often rely on the use of highly reactive (strong) dopants8-10, which are consumed during the doping process. Achieving efficient doping with weak and/or widely accessible dopants under mild conditions remains a considerable challenge. Here, we report a previously undescribed concept for the photocatalytic doping of OSCs that uses air as a weak oxidant (p-dopant) and operates at room temperature. This is a general approach that can be applied to various OSCs and photocatalysts, yielding electrical conductivities that exceed 3,000 S cm-1. We also demonstrate the successful photocatalytic reduction (n-doping) and simultaneous p-doping and n-doping of OSCs in which the organic salt used to maintain charge neutrality is the only chemical consumed. Our photocatalytic doping method offers great potential for advancing OSC doping and developing next-generation organic electronic devices.

A Highly Conductive n-Type Conjugated Polymer Synthesized in Water.

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a benchmark hole-transporting (p-type) polymer that finds applications in diverse electronic devices. Most of its success is due to its facile synthesis in water, exceptional processability from aqueous solutions, and outstanding electrical performance in ambient. Applications in fields like (opto-)electronics, bioelectronics, and energy harvesting/storage devices often necessitate the complementary use of both p-type and n-type (electron-transporting) materials. However, the availability of n-type materials amenable to water-based polymerization and processing remains limited. Herein, we present a novel synthesis method enabling direct polymerization in water, yielding a highly conductive, water-processable n-type conjugated polymer, namely, poly[(2,2'-(2,5-dihydroxy-1,4-phenylene)diacetic acid)-stat-3,7-dihydrobenzo[1,2-b:4,5-b']difuran-2,6-dione] (PDADF), with remarkable electrical conductivity as high as 66 S cm-1, ranking among the highest for n-type polymers processed using green solvents. The new n-type polymer PDADF also exhibits outstanding stability, maintaining 90% of its initial conductivity after 146 days of storage in air. Our synthetic approach, along with the novel polymer it yields, promises significant advancements for the sustainable development of organic electronic materials and devices.

Hydrogen Sulfide Splitting into Hydrogen and Sulfur through Off-Field Electrocatalysis.

Hydrogen sulfide (H2S), a toxic gas abundant in natural gas fields and refineries, is currently being removed mainly via the Claus process. However, the emission of sulfur-containing pollutants is hard to be prevented and the hydrogen element is combined to water. Herein, we report an electron-mediated off-field electrocatalysis approach (OFEC) for complete splitting of H2S into H2 and S under ambient conditions. Fe(III)/Fe(II) and V(II)/V(III) redox mediators are used to fulfill the cycles for H2S oxidation and H2 production, respectively. Fe(III) effectively removes H2S with almost 100% conversion during its oxidation process. The H+ ions are reduced by V(II) on a nonprecious metal catalyst, tungsten carbide. The mediators are regenerated in an electrolyzer at a cell voltage of 1.05 V, close to the theoretical potential difference (1.02 V) between Fe(III)/Fe(II) and V(II)/V(III). In a laboratory bench-scale plant, the energy consumption for the production of H2 from H2S is estimated to be 2.8 kWh Nm-3 H2 using Fe(III)/Fe(II) and V(II)/V(III) mediators and further reduced to about 0.5 kWh Nm-3 H2 when employing well-designed heteropolyacid/quinone mediators. OFEC presents a cost-effective approach for the simultaneous production of H2 and elemental sulfur from H2S, along with the complete removal of H2S from industrial processes. It also provides a practical platform for electrochemical reactions involving solid precipitation and organic synthesis.

On-Demand Catalysed n-Doping of Organic Semiconductors.

A new approach to control the n-doping reaction of organic semiconductors is reported using surface-functionalized gold nanoparticles (f-AuNPs) with alkylthiols acting as the catalyst only upon mild thermal activation. To demonstrate the versatility of this methodology, the reaction of the n-type dopant precursor N-DMBI-H with several molecular and polymeric semiconductors at different temperatures with/without f-AuNPs, vis-à-vis the unfunctionalized catalyst AuNPs, was investigated by spectroscopic, morphological, charge transport, and kinetic measurements as well as, computationally, the thermodynamic of catalyst activation. The combined experimental and theoretical data demonstrate that while f-AuNPs is inactive at room temperature both in solution and in the solid state, catalyst activation occurs rapidly at mild temperatures (~70 °C) and the doping reaction completes in few seconds affording large electrical conductivities (~10-140 S cm-1). The implementation of this methodology enables the use of semiconductor+dopant+catalyst solutions and will broaden the use of the corresponding n-doped films in opto-electronic devices such as thin-film transistors, electrochemical transistors, solar cells, and thermoelectrics well as guide the design of new catalysts.

Rapidly Constructing Sodium Fluoride-Rich Interface by Pressure and Diglyme-Induced Defluorination Reaction for Stable Sodium Metal Anode.

Sodium (Na) metal is able to directly use as a battery anode but have a highly reductive ability of unavoidably occurring side reactions with organic electrolytes, resulting in interfacial instability as a primary factor in performance decay. Therefore, building stable Na metal anode is of utmost significance for both identifying the electrochemical performance of laboratory half-cells employed for quantifying samples and securing the success of room-temperature Na metal batteries. In this work, we propose an NaF-rich interface rapidly prepared by pressure and diglyme-induced defluorination reaction for stable Na metal anode. Once the electrolyte is dropped into the coin-type cells followed by a slight squeeze, the Na metal surface immediately forms a protective layer consisting of amorphous carbon and NaF, effectively inhibiting the dendrite growth and dead Na. The resultant Na metal anode exhibits a long-term cycling lifespan over 1800 h even under the area capacity of 3.0 mAh cm-2 . Furthermore, such a universal and facile method is readily applied in daily battery assembly regarding Na metal anode.

Stabilizing Li4SnS4 Electrolyte from Interface to Bulk Phase with a Gradient Lithium Iodide/Polymer Layer in Lithium Metal Batteries.

Sulfide electrolytes promise superior ion conduction in all-solid-state lithium (Li) metal batteries, while suffering harsh hurdles including interior dendrite growth and instability against Li and moist air. A prerequisite for solving such issues is to uncover the nature of the Li/sulfide interface. Herein, air-stable Li4SnS4 (LSS) as a prototypical sulfide electrolyte is selected to visualize the dynamic evolution and failure of the Li/sulfide interface by cryo-electron microscopy. The interfacial parasitic reaction (2Li + 2Li4SnS4 = 5Li2S + Sn2S3) is validated by direct detection of randomly distributed Li2S and Sn2S3 crystals. A bifunctional buffering layer is consequently introduced by self-diffusion of halide into LSS. Both the interface and the grain boundaries in LSS have been stabilized, eliminating the growing path of Li dendrites. The buffering layer enables the durability of Li symmetric cell (1500 h) and high-capacity retention of the LiFePO4 full-cell (95%). This work provides new insights into the hierarchical design of sulfide electrolytes.

Soybean Protein Fiber Enabled Controllable Li Deposition and a LiF-Nanocrystal-Enriched Interface for Stable Li Metal Batteries.

The proliferation of lithium (Li) dendrites stemming from uncontrollable Li deposition seriously limits the practical application of Li metal batteries. The regulation of uniform Li deposition is thus a prerequisite for promoting a stable Li metal anode. Herein, a commercial lithiophilic skeleton of soybean protein fiber (SPF) is introduced to homogenize the Li-ion flux and induce the biomimetic Li growth behavior. Especially, the SPF can promote the formation of a LiF-nanocrystal-enriched interface upon cycling, resulting in low interfacial impedance and rapid charge transfer kinetics. Finally, the SPF-mediated Li metal anode can achieve high Coulombic efficiency of 98.7% more than 550 cycles and a long-term lifespan over 3400 h (∼8500 cycles) in symmetric tests. Furthermore, the practical pouch cell modified with SPF can maintain superior electrochemical performance over 170 cycles under a low N/P ratio and high mass loading of the cathode.

Visualizing the Sensitive Lithium with Atomic Precision: Cryogenic Electron Microscopy for Batteries.

Lithium (Li)-metal batteries are one of the most promising candidates for the next-generation energy storage devices due to their ultrahigh theoretical capacity. The realistic development of a Li metal battery is greatly impeded by the uncontrollable dendrite proliferation upon the chemically active metallic Li. To visualize the micromorphology or even the atomic structure of Li deposits is undoubtedly crucial, while imaging the sensitive Li still faces a huge challenge technically.Cryogenic electron microscopy (cryo-EM), an emerging imagery technology renowned for structural elucidation of biomaterials, is offering increased possibilities for analyzing sensitive battery materials reaching subangstrom resolution. Particularly for revealing metallic Li, cryo-EM exhibits remarkable superiority compared with the conventional electron imaging technique. On the one hand, cryo-EM could prevent the low melting-point Li metal from being damaged by the high electron dose induced thermal effect. On the other hand, the extremely low temperature immensely retards the rate of the side reaction where the Li reacts with the atmosphere or water vapor before the vacuum state. Consequently, the cryo-EM could acquire a high-resolution image of electron-beam sensitive Li in its native state at the nano- or even atomic scale, thus benefiting the fundamental perception and rational design of Li metal anodes.Thus, in this Account, we aim to highlight the significance of cryo-EM in analyzing metallic Li and developing a high-performance Li metal battery. We focus on how highly resolved cryo-EM realizes the breakthrough in detecting the crucial evolution during battery cycling, e.g., lattice ordering of Li, nanostructures of the solid electrolyte interphase (SEI), nucleation sites, and interface between the solid electrolyte and the Li anode. First, we briefly summarize the progress of Li metal imaging by cryo-EM in a timed sequence. In particular, the recent studies from our group are classified in order to systematically delineate the advantages that cryo-transmission electron microscopy (cryo-TEM) addressed on understanding and developing the Li metal battery. Second, the efforts of exhibiting the long-range ordering Li lattice are described to cognize the crystal orientation of both Li dendrites and uniform spheres. Subsequently, the nanostructures of SEI detected by cryo-TEM, maybe the most key information during Li plating/stripping, are systematically summarized. Benefitting from the subangstrom visualization on the newly formed and the particular inactive SEI after long-term cycling, we emphasize cryo-TEM's guidance in designing a robust, highly Li+ conductive, and Li-restoration facilitated SEI. We then propose the strategy of introducing a nucleation-site to enable uniform Li deposition by showing the evidence of Li nucleation atomically monitored through cryo-TEM. Moreover, the series of the work of atomic imagery and corresponding optimization of the interfaces between the polymer-based solid electrolyte and the Li anode are concluded. Finally, critical perspectives about the further step of cryo-TEM in the realistic development of high-energy density battery systems are also succinctly reviewed.

Precursor Engineering to Reduce Processing Temperature of ZnO Films for Flexible Organic Solar Cells.

Sol-gel-derived ZnO is one of the most widely used electron-transport layers in inverted organic solar cells. The sol-gel ZnO precursor consists of zinc acetate dehydrate (ZAH) and ethanolamine dissolved in 2-methoxyethanol, where ethanolamine chelates with ZAH, which helps ZAH dissolve in the 2-methoxyethanol. However, an annealing temperature above 120 °C is required to convert the complexes into ZnO. High temperatures are incompatible with flexible plastic substrates such as polyethylene terephthalate. In this work, we report an amine-free recipe consisting of ZAH in methanol to prepare ZnO films. The complex formed in the amine-free precursor solution is methanol-solvated ZAH, which is simpler than that of the amine-containing precursor solution. The temperature required for converting the precursor complex into ZnO was reduced to 90 °C for the amine-free recipe. Low-temperature-processed ZnO can function efficiently as an electron-transport layer in both rigid and flexible inverted nonfullerene solar cells.

Chlorine-Incorporation-Induced Formation of the Layered Phase for Antimony-Based Lead-Free Perovskite Solar Cells.

The environmental toxicity of Pb in organic-inorganic hybrid perovskite solar cells remains an issue, which has triggered intense research on seeking alternative Pb-free perovskites for solar applications. Halide perovskites based on group-VA cations of Bi3+ and Sb3+ with the same lone-pair ns2 state as Pb2+ are promising candidates. Herein, through a joint experimental and theoretical study, we demonstrate that Cl-incorporated methylammonium Sb halide perovskites (CH3NH3)3Sb2ClXI9-X show promise as efficient solar absorbers for Pb-free perovskite solar cells. Inclusion of methylammonium chloride into the precursor solutions suppresses the formation of the undesired zero-dimensional dimer phase and leads to the successful synthesis of high-quality perovskite films composed of the two-dimensional layered phase favored for photovoltaics. Solar cells based on the as-obtained (CH3NH3)3Sb2ClXI9-X films reach a record-high power conversion efficiency over 2%. This finding offers a new perspective for the development of nontoxic and low-cost Sb-based perovskite solar cells.

Efficient Colorful Perovskite Solar Cells Using a Top Polymer Electrode Simultaneously as Spectrally Selective Antireflection Coating.

Organometal halide perovskites have shown excellent optoelectronic properties and have been used to demonstrate a variety of semiconductor devices. Colorful solar cells are desirable for photovoltaic integration in buildings and other aesthetically appealing applications. However, the realization of colorful perovskite solar cells is challenging because of their broad and large absorption coefficient that commonly leads to cells with dark-brown colors. Herein, for the first time, we report a simple and efficient strategy to achieve colorful perovskite solar cells by using the transparent conducting polymer (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS) as a top electrode and simultaneously as an spectrally selective antireflection coating. Vivid colors across the visible spectrum are attained by engineering optical interference effects among the transparent PEDOT:PSS polymer electrode, the hole-transporting layer and the perovskite layer. The colored perovskite solar cells display power conversion efficiency values from 12.8 to 15.1% (from red to blue) when illuminated from the FTO glass side and from 11.6 to 13.8% (from red to blue) when illuminated from the PEDOT:PSS side. The new approach provides an advanced solution for fabricating colorful perovskite solar cells with easy processing and high efficiency.

Free-Standing Conducting Polymer Films for High-Performance Energy Devices.

Thick, uniform, easily processed, highly conductive polymer films are desirable as electrodes for solar cells as well as polymer capacitors. Here, a novel scalable strategy is developed to prepare highly conductive thick poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (HCT-PEDOT:PSS) films with layered structure that display a conductivity of 1400 S cm(-1) and a low sheet resistance of 0.59 ohm sq(-1). Organic solar cells with laminated HCT-PEDOT:PSS exhibit a performance comparable to the reference devices with vacuum-deposited Ag top electrodes. More importantly, the HCT-PEDOT:PSS film delivers a specific capacitance of 120 F g(-1) at a current density of 0.4 A g(-1). All-solid-state flexible symmetric supercapacitors with the HCT-PEDOT:PSS films display a high volumetric energy density of 6.80 mWh cm(-3) at a power density of 100 mW cm(-3) and 3.15 mWh cm(-3) at a very high power density of 16160 mW cm(-3) that outperforms previous reported solid-state supercapacitors based on PEDOT materials.

Anode-Free Sodium Metal Pouch Cell Using Cu3P Nanowires In Situ Grown on Current Collector.

Anode-free sodium metal battery (AFSMB) promises high energy density but suffers from the difficulty of maintaining high cycling stability. Nonuniform sodium (Na) deposition on the current collector is largely responsible for capacity decay in the cycling process of AFSMB. Here, a unique copper phosphide (Cu3P) nanowire is constructed on copper (Cu3P@Cu) as a sodium deposition substrate by an in situ growth method. Superior electrochemical performance of Cu3P@Cu anode is delivered in asymmetric cells with an average Coulombic efficiency of 99.8% for over 800 cycles at 1 mA cm-2 with 1 mA h cm-2. The symmetric cell of Cu3P@Cu displayed a cycling lifespan of over 2000 h at 2 mA cm-2 with 1 mA h cm-2. Cryo-transmission electron microscope characterization and first principles calculation revealed that the low Na+ absorption energy and low Na+ diffusion energy barrier on Na3P promoted uniform Na nucleation and deposition, thus enhancing the Na surface stability. Moreover, anode-free Na3V2(PO4)3//Cu3P@Cu full pouch cell delivered a considerable cycling capacity of ≈15 mA h in 170 cycles, demonstrating its practical feasibility.

Regulating Grind-Induced Lattice Distortion for Nickel-Rich Cathodes by Annealing.

The commercialization of high-performance nickel-rich cathodes always awaits a cost-effective, environmentally friendly, and large-scale preparation method. Despite a grinding process normally adopted in the synthesis of the nickel-rich cathodes, lattice distortion, rough surface, and sharp edge transformation inevitably occurr in the resultant samples. In this work, an additional annealing process is proposed that aims at regulating lattice distortion as well as achieving round and smoother morphologies without any structural or elemental modifications. Such a structural enhancement is favored for improved lithium diffusion and electrochemical stability during cycling. Consequently, the annealed cathodes demonstrate a considerable enhancement in capacity retention, escalating from 68.7% to 91.9% after 100 cycles at 1 C. Additionally, the specific capacity is significantly increased from 64 to 142 mAh g-1 at 5 C when compared to the unannealed cathodes. This work offers a straightforward and effective approach for reinforcing the electrochemical properties of nickel-rich cathodes.

First-Principles Study on Polymer Electrolyte Interface Engineering for Lithium Metal Anodes.

Modifying the interface between the lithium metal anode (LMA) and the electrolyte is crucial for achieving high-performance lithium metal batteries (LMBs). Recent research indicates that altering Li-metal interfaces with polymer coatings is an effective approach to extend LMBs' cycling lifespan. However, the physical properties of these polymer-Li interfaces have not yet been fully investigated. Therefore, the structural stability, electronic conductivity, and ionic conductivity of polymer-Li interfaces were examined based on first-principles calculations in this study. Several representative polymer compounds utilized in LMBs were assessed, including polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyethylene oxide (PEO). Our research revealed that lithium fluoride is formed upon fluoropolymer degradation, explaining previously observed experimental results. Polymers containing nitrile groups exhibit strong adhesion to lithium metal, facilitating the formation of the stable interface layer. Regarding electronic conductivity, the fluoropolymers preserve a good insulating property, which diminished marginally in the presence of lithium, but that of PAN and PEO significantly reduces. Additionally, lithium diffusion on PTFE and PEO demonstrates low diffusion barriers and high coefficients, enabling easy transportation. Overall, our investigation reveals that the interfaces formed between various polymers and LMA have distinct characteristics, providing new fundamental insights for designing composites with tailored interface properties.

Reducing Gases Triggered Cathode Surface Reconstruction for Stable Cathode-Electrolyte Interface in Practical All-Solid-State Lithium Batteries.

The interfacial compatibility between cathodes and sulfide solid-electrolytes (SEs) is a critical limiting factor of electrochemical performance in all-solid-state lithium-ion batteries (ASSLBs). This work presents a gas-solid interface reduction reaction (GSIRR), aiming to mitigate the reactivity of surface oxygen by inducing a surface reconstruction layer (SRL) . The application of a SRL, CoO/Li2 CO3 , onto LiCoO2 (LCO) cathode results in impressive outcomes, including high capacity (149.7 mAh g-1 ), remarkable cyclability (retention of 84.63% over 400 cycles at 0.2 C), outstanding rate capability (86.1 mAh g-1 at 2 C), and exceptional stability in high-loading cathode (28.97 and 23.45 mg cm-2 ) within ASSLBs. Furthermore, the SRL CoO/Li2 CO3 enhances the interfacial stability between LCO and Li10 GeP2 S12 as well as Li3 PS4 SEs. Significantly, the experiments suggest that the GSIRR mechanism can be broadly applied, not only to LCO cathodes but also to LiNi0.8 Co0.1 Mn0.1 O2 cathodes and other reducing gases such as H2 S and CO, indicating its practical universality. This study highlights the significant influence of the surface chemistry of the oxide cathode on interfacial compatibility, and introduces a surface reconstruction strategy based on the GSIRR process as a promising avenue for designing enhanced ASSLBs.

Industrial Kraft Lignin Based Binary Cathode Interface Layer Enables Enhanced Stability in High Efficiency Organic Solar Cells.

Herein, a binary cathode interface layer (CIL) strategy based on the industrial solvent fractionated LignoBoost kraft lignin (KL) is adopted for fabrication of organic solar cells (OSCs). The uniformly distributed phenol moieties in KL enable it to easily form hydrogen bonds with commonly used CIL materials, i.e., bathocuproine (BCP) and PFN-Br, resulting in binary CILs with tunable work function (WF). This work shows that the binary CILs work well in OSCs with large KL ratio compatibility, exhibiting equivalent or even higher efficiency to the traditional CILs in state of art OSCs. In addition, the combination of KL and BCP significantly enhanced OSC stability, owing to KL blocking the reaction between BCP and nonfullerene acceptors (NFAs). This work provides a simple and effective way to achieve high-efficient OSCs with better stability and sustainability by using wood-based materials.

Electrochemical Restoration of Battery Materials Guided by Synchrotron Radiation Technology for Sustainable Lithium-Ion Batteries.

Lithium-ion batteries (LIBs) have been ubiquitous in modern society, especially in the fields of electronic devices, electric vehicles and grid storage, while raising concerns about a tremendous number of spent batteries in the next five to ten years. As environmental awareness and resource security is gaining increasingly extensive attention, how to effectively deal with spent LIBs has become a challenging issue academically and industrially. Accordingly, the development of battery recycling has surfaced as a highly researched topic in the battery community. Recently, the structural and electrochemical restoration of recycled electrode materials have been proposed as a non-destructive method to save more energy and chemical agents compared with mature metallurgical methods. Such a refurbishment process of electrode materials is also regarded as a reverse process of their degradation in the working condition. Notably, synchrotron radiation technology, which is previously applied to diagnose battery degrade, has started to play major roles in gaining more insight into the structural restoration of electrode materials. Here, the contribution of synchrotron radiation technology to reveal the underlying degradation and regeneration mechanisms of LIBs cathodes is highlighted, providing a theoretical basis and guidance for the direct recycling and reuse of degraded cathodes.

Stable organic electrochemical neurons based on p-type and n-type ladder polymers.

Organic electrochemical transistors (OECTs) are a rapidly advancing technology that plays a crucial role in the development of next-generation bioelectronic devices. Recent advances in p-type/n-type organic mixed ionic-electronic conductors (OMIECs) have enabled power-efficient complementary OECT technologies for various applications, such as chemical/biological sensing, large-scale logic gates, and neuromorphic computing. However, ensuring long-term operational stability remains a significant challenge that hinders their widespread adoption. While p-type OMIECs are generally more stable than n-type OMIECs, they still face limitations, especially during prolonged operations. Here, we demonstrate that simple methylation of the pyrrole-benzothiazine-based (PBBT) ladder polymer backbone results in stable and high-performance p-type OECTs. The methylated PBBT (PBBT-Me) exhibits a 25-fold increase in OECT mobility and an impressive 36-fold increase in µC* (mobility × volumetric capacitance) compared to the non-methylated PBBT-H polymer. Combining the newly developed PBBT-Me with the ladder n-type poly(benzimidazobenzophenanthroline) (BBL), we developed complementary inverters with a record-high DC gain of 194 V V-1 and excellent stability. These state-of-the-art complementary inverters were used to demonstrate leaky integrate-and-fire type organic electrochemical neurons (LIF-OECNs) capable of biologically relevant firing frequencies of about 2 Hz and of operating continuously for up to 6.5 h. This achievement represents a significant improvement over previous results and holds great potential for developing stable bioelectronic circuits capable of in-sensor computing.

Ground-state electron transfer in all-polymer donor:acceptor blends enables aqueous processing of water-insoluble conjugated polymers.

Water-based conductive inks are vital for the sustainable manufacturing and widespread adoption of organic electronic devices. Traditional methods to produce waterborne conductive polymers involve modifying their backbone with hydrophilic side chains or using surfactants to form and stabilize aqueous nanoparticle dispersions. However, these chemical approaches are not always feasible and can lead to poor material/device performance. Here, we demonstrate that ground-state electron transfer (GSET) between donor and acceptor polymers allows the processing of water-insoluble polymers from water. This approach enables macromolecular charge-transfer salts with 10,000× higher electrical conductivities than pristine polymers, low work function, and excellent thermal/solvent stability. These waterborne conductive films have technological implications for realizing high-performance organic solar cells, with efficiency and stability superior to conventional metal oxide electron transport layers, and organic electrochemical neurons with biorealistic firing frequency. Our findings demonstrate that GSET offers a promising avenue to develop water-based conductive inks for various applications in organic electronics.