Effect of multilayer SnO₂ architectures on charge transport and optical properties in triple-cation perovskite solar cells

Triple-cation halide perovskites have emerged as highly promising absorbers for perovskite solar cells (PSCs) owing to their excellent intrinsic optoelectronic properties. Nevertheless, challenges such as device instability and current-voltage hysteresis, often originating from hydroxyl-rich electron transport layers (ETLs) like ZnO and TiO₂, continue to hinder device performance. In this work, SnO₂-based ETLs with different layer architectures were engineered and integrated into planar PSCs (FTO/SnO₂/perovskite/Spiro-OMeTAD/Ag) to mitigate these limitations. Three ETL configurations were investigated: a reference bilayer comprising one amorphous and one crystalline SnO₂ layer (1A1C), a single amorphous layer with a double crystalline stack (1A2C), and a double amorphous layer with a single crystalline layer (2A1C). Comprehensive structural, optical, and photovoltaic analyses revealed that the 1A2C configuration delivered the best performance, achieving a power conversion efficiency (PCE) of 15.33% (V_OC = 1.04 V, J_SC = 15.46 mA cm⁻² and FF = 71.50%), compared to 12.16% for the 1A1C reference. The superior efficiency of the 1A2C device is attributed to improved charge transport layer and suppressed carrier recombination at the ETL/perovskite interface, arising from optimized ETL architecture. This study demonstrates a simple yet effective route for enhancing PSC efficiency and stability, offering valuable insights for advancing perovskite device engineering.