Copper nanowire (CuNW)-network film is a promising alternative to the conventional indium tin oxide (ITO) as a transparent conductor. However, thermal instability and the ease of oxidation hinder the practical applications of CuNW films. We present oxidation-resistive CuNW-based composite electrodes that are highly transparent, conductive and flexible. Lactic acid treatment effectively removes both the organic capping molecule and the surface oxide/hydroxide from the CuNWs, allowing direct contact between the nanowires. This chemical approach enables the fabrication of transparent electrodes with excellent properties (19.8 Ω sq−1 and 88.7% at 550 nm) at room temperature without any atmospheric control. Furthermore, the embedded structure of CuNWs with Al-doped ZnO (AZO) dramatically improves the thermal stability and oxidation resistance of CuNWs. These AZO/CuNW/AZO composite electrodes exhibit high transparency (83.9% at 550 nm) and low sheet resistance (35.9 Ω sq−1), maintaining these properties even with a bending number of 1280 under a bending radius of 2.5 mm. When implemented in a Cu(In1−x,Gax)(S,Se)2 thin-film solar cell, this composite electrode demonstrated substantial potential as a low-cost (Ag-, In-free), high performance transparent electrode, comparable to a conventional sputtered ITO-based solar cell. A highly thermal and oxidation-resistive AZO/Cu nanowire/AZO composite electrode for thin-film solar cells was fabricated at room temperature without any atmospheric control. Our novel transparent composite electrode showed good thermal oxidation stability as well as high conductivity (∼35.9 Ω/sq), transparency (83.9% at 550 nm) and flexibility. Metal nanowire-based materials are promising alternatives to the conventional transparent electrodes found in solar cells and touchscreen displays because they are naturally flexible and stretchable — attributes that can dramatically improve device lifetimes. Current efforts, however, have been hampered by the need for expensive silver nanowires; lower-cost materials, such as copper nanowires, possess an insulating surface oxide film that deteriorates device conductivity. Jooho Moon and co-workers from Yonsei University, South Korea, have now uncovered a surprising way to remove oxides and organic capping molecules from copper nanowires using lactic acid, a biomolecule commonly found in milk. Room temperature lactic acid treatments, followed by washes with organic solvents, yielded transparent copper nanowire networks that feature direct, metal-to-metal contact. Photovoltaic testing revealed these bendable electrodes had excellent conductivity for high-performance solar applications.
Using a thermally crosslinkable organosiloxane-based organic−inorganic hybrid material, we formulated a functional ink suitable for ink-jet printing of dielectric thin films. Ink solvent chemistry plays an important role in producing a uniform dielectric layer. In particular, the hydrodynamic motion of the solvents is controlled during the drying period. We used a higher-boiling-point solvent in order both to prevent a nozzle from clogging and to suppress convective flow. We also incorporated a lower-boiling-point solvent of high surface tension for diminishing the outward Marangoni flow. We successfully applied the printed hybrid dielectric layer with smooth surface morphology to the gate dielectric layer for organic thin-film transistors and analyzed the electrical performance of the transistor based on the ink-jet-printed dielectric layer, comparing with that of the transistor based on the spin-coated dielectric layer.
Aqueous Cu nanoparticles are synthesized using a reducing agent and surface capping molecule which prevents the interparticular agglomeration and surface oxidation. Aqueous conductive nano ink is prepared using the resulting Cu nanoparticles and conductive Cu layers are prepared via a wet coating process. The conductive Cu layers, metalized by annealing at 300 degrees C under vacuum atmosphere, exhibit excellent electrical resistivity, showing values as low as 12 microomega cm. The long-term dispersion stability for three months is monitored through an investigation on the rheological behavior of the conductive nano ink and the resistivity variation of the conductive Cu layer. The adhesion property of the conductive Cu layer is dramatically improved when using a primer-treated polyimide film, whereas the conductive Cu layer completely peels off on a pristine polyimide film. The epoxy-contained primer plays a critical role as an intermediary between the aqueous Cu nano ink and the polyimide film.
Among various candidate materials, Cu2ZnSnS4 (CZTS) is a promising earth-abundant semiconductor for low-cost thin film solar cells. We report a facile, less toxic, highly concentrated synthetic method utilizing the heretofore unrecognized, easily decomposable capping ligand of triphenylphosphate, where phase-pure, single-crystalline, and well-dispersed colloidal CZTS nanocrystals were obtained. The favorable influence of the easily decomposable capping ligand on the microstructural evolution of device-quality CZTS absorber layers was clarified based on a comparative study with commonly used oleylamine-capped CZTS nanoparticles. The resulting CZTS nanoparticles enabled us to produce a dense and crack-free absorbing layer through annealing under a N2 + H2S (4%) atmosphere, demonstrating a solar cell with an efficiency of 3.6% under AM 1.5 illumination.
We report novel salami-like core-sheath composites consisting of Si nanoparticle assemblies coated with indium tin oxide (ITO) sheath layers that are synthesized via coelectrospinning. Core-sheath structured Si nanoparticles (NPs) in static ITO allow robust microstructures to accommodate for mechanical stress induced by the repeated cyclical volume changes of Si NPs. Conductive ITO sheaths can provide bulk conduction paths for electrons. Distinct Si NP-based core structures, in which the ITO phase coexists uniformly with electrochemically active Si NPs, are capable of facilitating rapid charge transfer as well. These engineered composites enabled the production of high-performance anodes with an excellent capacity retention of 95.5% (677 and 1523 mAh g(-1,) which are based on the total weight of Si-ITO fibers and Si NPs only, respectively), and an outstanding rate capability with a retention of 75.3% from 1 to 12 C. The cycling performance and rate capability of core-sheath-structured Si NP-ITO are characterized in terms of charge-transfer kinetics.
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