Crystallization Behavior of Ambient-Air-Processed CsPbBr ₃ Thin Films on Various Electron Transport Layers and Its Impact on Solar Cell Performance

CsPbBr3 perovskite is a promising wide-bandgap semiconductor for photovoltaic applications, but its crystallization dynamics and charge transport properties are highly dependent on interfacial interactions with electron transport layers (ETLs). This study systematically investigates the influence of ETLs: SnO2, TiO2, and In2S3, on the crystallization, morphology, and photovoltaic performance of CsPbBr3 thin films processed under ambient-air conditions. The choice of ETL is found to significantly affect the structural evolution of the PbBr2 precursor and the final CsPbBr3 film, impacting the device efficiency. Among the studied ETLs, SnO2 promotes the formation of compact and uniform CsPbBr3 films, leading to the highest power conversion efficiency (PCE) of 5.05%. In comparison, TiO2-based devices exhibit a moderate efficiency of 3.44% due to suboptimal film flatness, whereas In2S3 results in small-grained films with high defect densities, limiting the efficiency to 0.70%. Photoluminescence and impedance spectroscopy analyses further confirm that SnO2 effectively suppresses defect-mediated recombination, enhancing charge transport and extraction. These findings underscore the crucial role of ETL selection in optimizing CsPbBr3 crystallization and provide valuable insights for developing efficient wide-bandgap perovskite solar cells under ambient conditions.