Recently, metal nanowires have been actively researched as a novel form of conductive material for application in various electronic devices, and Cu nanowire has gained much attention due to its high electrical conductivity and low cost. In this report, we present a study on the synthesis of high aspect ratio and high yield Cu NWs using Cu oxalate as a Cu precursor, which can be differentiated from the conventional approaches. Cu oxalate would be able to minimize the composition change in the reaction solution during the synthesis by generating CO_2 gas as a reaction by-product, which is easy to remove during Cu NW synthesis promoting the synthesis of uniform and high aspect ratio Cu NWs. In this work, we successfully demonstrated that the high reduction temperature of Cu oxalate, 250 °C, which is considered to be a main limiting factor for the application of Cu oxalate as a Cu precursor, can be effectively reduced to produce Cu-ions at the considerably low temperature, 160 °C, by adding ascorbic acid into the reaction solution. In addition, PVP and NaCl were introduced as a capping and mediating agent for the synthesis of high aspect ratio Cu NWs, and the effects of each agent were studied to determine the optimal addition conditions. In this study, various physical and chemical characterizations, including field-emission scanning electron microscopy, X-ray diffractometer, energy-dispersive X-ray spectroscopy, focused ion beam, field-emission scanning transmission electron microscopy, and selected-area electron diffraction analysis, were performed to analyze and evaluate the synthesized Cu NWs, which successfully demonstrated that our novel approach would produce a high aspect ratio Cu NWs, 413, with a diameter of 189 nm and a length of 78 μm with 110 orientation growth. In addition, the high synthesis yield, 94

In this study, we investigate the impact of incorporating poly(acrylic acid) (PAA) as a soft polymer on the longterm stability and flexibility (or stretchability) of a highly conductive composite consisting of hydroquinone (HQ)-modified Poly(3,4-ethylenedioxythiophene): poly(styrene-sulfonate) (HQ-PEDOT:PSS). Our findings demonstrate that PAA can effectively act as a steric hindrance barrier between conductive-PEDOT and insulativePSS, thus improving the stability of the composite over time. Furthermore, the PAA mixture minimizes the conductivity decrease compared to other representative hydrophilic soft polymers, such as poly(vinyl alcohol) (PVA) and poly(vinylpyrrolidone) (PVP). With the addition of 2 wt% PAA to HQ-PEDOT:PSS, the composite exhibits significantly higher conductivity (290 S/cm) compared to PVA (42 S/cm) and PVP (10-3 S/cm). The HQPEDOT:PSS/PAA composite also displays excellent stretchability, with a sharp strain response followed by a drastically enhanced gauge factor over a wide strain range (10%-50%). As a result, the composite shows great potential as a strain sensor, with high sensitivity for detecting diverse body motions. Moreover, due to its high conductivity, the composite exhibits high sensitivity for detecting human electrocardiogram (ECG) signals, with negligible degradation of signal intensity even one month after fabrication. Overall, our results suggest that the HQ-PEDOT:PSS/PAA conductive composite has significant potential for wearable smart textile applications, enabling diverse body motion and vital sign sensing.

In this study, we fabricated Si-based heterojunction solar cells (HSCs) with an asymmetric TMO–metal–TMO (TMT) structure using both MoO3 and V2O5 as the hole-selective contacts. Our HSCs offer enhanced long-term stability and effective passivation for crystal defects on the Si sur-face. We analyzed the oxygen vacancy state and surface morphology of the MoO3- and V2O5-TMO thin films using X-ray photoelectron spectroscopy and atomic force microscopy to investigate their passivation characteristics for Si surface defects. From the measured minority carrier lifetime, V2O5 revealed a highly improved lifetime (590 μs) compared to that of MoO3 (122.3 μs). In addition, we evaluated the long-term stability of each TMO thin film to improve the operation stability of the HSCs. We deposited different types of TMOs as the top- and bottom-TMO layers and assessed the effect of the thickness of each TMO layer. The fabricated asymmetric TMT/Si HSCs showed noticeable improvements in efficiency (7.57%) compared to 6.29% for the conventional symmetric structure which used the same TMO material for both the top and bottom layers. Furthermore, in terms of long-term stability, the asymmetric TMT/Si HSCs demonstrated an efficiency that was 250% higher than that of symmetric TMT/Si HSCs, as determined via power conversion efficiency degradation over 2000 h which is mainly attributed by the lower oxygen vacancy of the top-TMO, V2O5. These results suggest that the asymmetric TMT structure is a promising approach for the fabrication of low-cost and high-efficiency Si-based HSCs with enhanced long-term stability.