Liquid Metal-Based Perovskite Solar Cells: In Situ Formed Gallium Oxide Interlayer Improves Stability and Efficiency

In this study, eutectic gallium–indium alloy (EGaIn) liquid metal is used as the rear electrode for perovskite solar cells (PSCs), where the interfacial properties of the device, particularly the beneficial roles of the surface oxide of the liquid metal, are explored. The findings demonstrate that the native oxide of the EGaIn electrode significantly affects the stability of photovoltaic performance and impedance characteristics including series and shunt resistances. Based on the results, the following hypothesis is formulated: the oxide interlayer serves two crucial functions of a barrier against metal diffusion and a tunnel for enhancing charge extraction and transfer. The results of elemental mapping and trap density calculation support the former function of the hypothesis that the oxide film can effectively prevent metal penetration into the perovskite layer. Furthermore, measurements involving capacitance−voltage and time-resolved photoluminescence confirm that the oxide film on the liquid metal eliminates the interfacial Schottky barrier, promoting efficient charge extraction and transfer processes. Finally, the investigation is extended to develop flexible PSCs using the EGaIn electrode, which consistently exhibits stable performance during repeated bending cycles. Notably, the EGaIn rear electrode can be readily removed and collected through a straightforward acid treatment, offering a promising avenue for efficient cell recycling.