High Operation Stability of Solution-Processed Ultrathin (<1μm) Flexible Transparent Electrodes with Wire-Particle Nano-Adhesion between Metal and Metal-Oxide-Semiconductor

Ultrathin flexible transparent electrodes (<i>u</i>FTEs) are an indispensable component in emerging flexible electronics due to a high level of compatibility and comfortability while there is an ever-increasing demand for low-cost solution-process-based high-throughput production for <i>u</i>FTEs. Owing to the successful advances of solution-processed nanomaterials [1], <i>u</i>FTE composites from transparent metal-oxide-semiconductors (TMOS) and silver nanowires (<i>^Ag</i>NWs) have been extensively reported. However, there is still a big gap in achieving simultaneous multi-loading operations (i.e., folding cycles with &lt;1.5 mm radius of curvature, current bias with &gt;300 mA cm^-2, and humid environments at 85 % of relative humidity (RH)), which is highly required as one of the practically rigorous environments.<br/>The fundamental bottleneck is to achieve high-quality interfaces simultaneously by performing tri-system integration in <i>^Ag</i>NW-<i>^TMOS</i>NP hybrid <i>u</i>FTEs. The tri-system includes three different interfaces <i>^Ag</i>NW-<i>^Ag</i>NW, <i>^TMOS</i>NP-<i>^TMOS</i>NP, and <i>^Ag</i>NW-<i>^TMOS</i>NP. All interfaces play key roles in the long operational stability against the simultaneous multi-loading operations. Although excellent works have been reported in the individual systems of <i>^Ag</i>NW-<i>^Ag</i>NW networks [2] and TMOS-TMOS nanocrystal films [3], importantly, the quality of <i>^Ag</i>NW-<i>^TMOS</i>NP heterogeneous interfaces needs substantially improving due to the mismatched interaction between <i>^Ag</i>NW and <i>^TMOS</i>NP. As a consequence, there are primary need to realize the tri-system integration for achieving the mechanical, electrical, and chemical stability in the solution-processed <i>^Ag</i>NW-<i>^TMOS</i>NP composites for better <i>u</i>FTEs.<br/>In this study, we develop a simple one-step <i>in situ</i> solution processed method (<i>i</i>SPM) to fabricate the solution-processed tri-system-integrated <i>u</i>FTEs (greatly thin less than 1μm) composed of <i>^Ag</i>NWs and <i>^ZnO</i>NPs at room temperature. The <i>i</i>SPM is developed for both (i) removing the capping agents from <i>^Ag</i>NWs and (ii) facilitating <i>^ZnO</i>NPs with flexible geometric shapes through the course of the coalescence process. The provided condition from both (i) and (ii) enables the <i>^ZnO</i>NPs to be capable of in situ nano-adhesion into the cleaned surface of <i>^Ag</i>NWs via flexible geometric shapes. Fundamentally, we show the in-situ atomic passivating mechanism of <i>^Ag</i>NW by the liquid-like spreading dynamics of solid-state <i>^ZnO</i>NP being wetted on the <i>^Ag</i>NW surface. The nanonet <i>u</i>FTEs with <i>tri-system integration</i> via <i>i</i>SPM show very good mechanical-electrical-thermal-moisture stability of the current density fluctuations less than 5 % against simultaneous multi-loading fatigue tests (10,000 cyclic mechanical folding with approximately 0.5 mm of FR, continuous electrical bias of 8.4 MA cm^-2, and 85 % RH condition). The superior electrical/optical properties (&lt;10 Ω sq.^-1 of sheet resistance and &gt;88 % of diffused transmittance in the region of wavelengths 400-1000 nm) and smooth surface topography (within ~1 nm of RMS and ~5 nm of PtV roughness) have been achieved within all the <i>i</i>SPM-treated <i>^Ag</i>NW-<i>^ZnO</i>NP nanonet <i>u</i>FTEs. Consequently, our finding unveils the complex interfacial dynamics associated with the heterogeneous interface system between <i>^Ag</i>NWs and <i>^ZnO</i>NPs and holds great promise in understanding the in-situ nano-adhesion process and increasing the design flexibility of promising solution-processed <i>u</i>FTEs.<br/><b>Reference</b><br/>1. Huang, Z., Ouyang, D., Shih, C., Yang, B. and Choy, W. C. H. Solution-Processed Ternary Oxides as Carrier Transport/Injection Layers in Optoelectronics. <i>Adv. Energy Mater.</i> <b>10</b>, 1900903 (2020).<br/>2. Park, J. H. <i>et al.</i> Flash-Induced Self-Limited Plasmonic Welding of Silver Nanowire Network for Transparent Flexible Energy Harvester. <i>Adv. Mater.</i> <b>29</b>, 1603473 (2016).<br/>3. Chen, Z.<i> et al.</i> A Transparent Electrode Based on Solution-Processed ZnO for Organic Optoelectronic Devices. <i>Nat. Commun.</i> <b>13</b>, 4387 (2022).