Hierarchical Silver Network Transparent Conducting Electrodes for Thin-Film Solar Cells

Flexible metal network transparent conducting electrodes (TCEs) are expected to be the most promising candidates to replace indium tin oxide (ITO) due to their excellent electro-optical performance and mechanical flexibility. However, to successfully replace ITO with the metal network TCEs, more studies on their suitability for integration with real devices are needed. In this study, we developed a hierarchical silver network simultaneously meeting the requirements of (i) low sheet resistance, (ii) high optical transmittance, (iii) excellent mechanical flexibility, and (iv) good integration into a thin-film solar cell. The hierarchical silver network consists of a silver micromesh as the main framework and silver nanowires as the secondary framework. The hierarchical network provides a figure of merit similar to that of the individual micromesh and much higher than those of silver nanowires and ITO. When applied to Cu(In, Ga)Se-2 thin-film solar cells, the hierarchical network achieved better device performance than the micromesh. In the hierarchical network, the micromesh enables low sheet resistance and the silver nanowires enable excellent integration with the device while maintaining high optical transmittance. Thus, considering the aforementioned requirements, the hierarchical network could be one of the best candidates as a TCE for Cu(In, Ga)Se-2 thin-film solar cells.