Crystallization Behavior of Ambient-Air-Processed CsPbBr3 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.