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 (uFTEs) 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 uFTEs. Owing to the successful advances of solution-processed nanomaterials [1], uFTE composites from transparent metal-oxide-semiconductors (TMOS) and silver nanowires (^AgNWs) have been extensively reported. However, there is still a big gap in achieving simultaneous multi-loading operations (i.e., folding cycles with <1.5 mm radius of curvature, current bias with >300 mA cm^-2, and humid environments at 85 % of relative humidity (RH)), which is highly required as one of the practically rigorous environments.
The fundamental bottleneck is to achieve high-quality interfaces simultaneously by performing tri-system integration in ^AgNW-^TMOSNP hybrid uFTEs. The tri-system includes three different interfaces ^AgNW-^AgNW, ^TMOSNP-^TMOSNP, and ^AgNW-^TMOSNP. 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 ^AgNW-^AgNW networks [2] and TMOS-TMOS nanocrystal films [3], importantly, the quality of ^AgNW-^TMOSNP heterogeneous interfaces needs substantially improving due to the mismatched interaction between ^AgNW and ^TMOSNP. 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 ^AgNW-^TMOSNP composites for better uFTEs.
In this study, we develop a simple one-step in situ solution processed method (iSPM) to fabricate the solution-processed tri-system-integrated uFTEs (greatly thin less than 1μm) composed of ^AgNWs and ^ZnONPs at room temperature. The iSPM is developed for both (i) removing the capping agents from ^AgNWs and (ii) facilitating ^ZnONPs with flexible geometric shapes through the course of the coalescence process. The provided condition from both (i) and (ii) enables the ^ZnONPs to be capable of in situ nano-adhesion into the cleaned surface of ^AgNWs via flexible geometric shapes. Fundamentally, we show the in-situ atomic passivating mechanism of ^AgNW by the liquid-like spreading dynamics of solid-state ^ZnONP being wetted on the ^AgNW surface. The nanonet uFTEs with tri-system integration via iSPM 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 (<10 Ω sq.^-1 of sheet resistance and >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 iSPM-treated ^AgNW-^ZnONP nanonet uFTEs. Consequently, our finding unveils the complex interfacial dynamics associated with the heterogeneous interface system between ^AgNWs and ^ZnONPs and holds great promise in understanding the in-situ nano-adhesion process and increasing the design flexibility of promising solution-processed uFTEs.
Reference
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2. Park, J. H. et al. Flash-Induced Self-Limited Plasmonic Welding of Silver Nanowire Network for Transparent Flexible Energy Harvester. Adv. Mater. 29, 1603473 (2016).
3. Chen, Z. et al. A Transparent Electrode Based on Solution-Processed ZnO for Organic Optoelectronic Devices. Nat. Commun. 13, 4387 (2022).