Modulating Oxygen Vacancies in BaSnO₃ for Printable Carbon-Based Mesoscopic Perovskite Solar Cells

The mesoscopic electron transport layer (m-ETL) has been demonstrated to help perovskite solar cells (PSCs) construct a tough interface against stress and a good contact for efficient extraction of photogenerated electrons. The barium stannate BaSnO3 (BSO) has exhibited great potential to be applied as PSCs’ m-ETL. However, it lacks wide applications. Here, we report the synthesis of BSO nanoparticles with modulated crystallinity and oxygen vacancy distribution by controlling the heat treatment atmosphere during the synthesizing process via the co-precipitation method and demonstrate their applications as the m-ETL for printable hole-conductor-free carbon-based mesoscopic PSCs (p-MPSCs). We find that heat treatment under nitrogen greatly improves the crystallinity of BSO particles and brings oxygen vacancies, while annealing under oxygen leads to poor crystallinity but effectively eliminates the oxygen vacancies in BSO particles. The BSO particles are first heated in nitrogen to obtain better crystallization and dispersion and then cooled down in oxygen to reduce the surface defects. This heat treatment method could boost the power conversion efficiency (PCE) of p-MPSCs with the BSO m-ETL to 14.77%. However, the PCE values of devices based on BSO synthesized under nitrogen or oxygen alone are 11.94 and 6.86%, respectively.