Construction of Compact Methylammonium Bismuth Iodide Film Promoting Lead-Free Inverted Planar Heterojunction Organohalide Solar Cells with Open-Circuit Voltage over 0.8 V.

A bismuth-based organohalide material, methylammonium bismuth iodide (MABiI), has been recently explored as an efficient lead-free light absorber in photovoltaic applications. However, the poor surface morphology of the MABiI film fabricated via conventional one-step spin-coating methods has limited the performance of the device. In this work, a smooth, uniform, and compact MABiI thin film was realized by a novel two-step evaporation-spin-coating film fabrication strategy for the first time. Taking advantage of the superior MABiI thin film, the best-performing inverted planar heterojuncion photovoltaic device exhibited a power conversion efficiency of 0.39% with open-circuit voltage as high as 0.83 V, which demonstrated the lowest loss-in-potential to date in MABiI-based solar cells. Moreover, the facile film fabrication strategy utilized in this work paves the way for high reproducibility of lead-free organohalide films and devices.