Bismuth-based solar cells have exhibited some advantages over lead perovskite solar cells for nontoxicity and superior stability, which are currently two main concerns in the photovoltaic community. As for the perovskite-related compound (CHNH)BiI applied for solar cells, the conversion efficiency is severely restricted by the unsatisfactory photoactive film quality. Herein we report a novel two-step approach- high-vacuum BiI deposition and low-vacuum homogeneous transformation of BiI to (CHNH)BiI-for highly compact, pinhole-free, large-grained films, which are characterized with absorption coefficient, trap density of states, and charge diffusion length comparable to those of some lead perovskite analogues. Accordingly, the solar cells have realized a record power conversion of efficiency of 1.64% and also a high external quantum efficiency approaching 60%. Our work demonstrates the potential of (CHNH)BiI for highly efficient and long-term stable solar cells.

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There is a multitude of reports on different methods of fabricating organic–inorganic halide perovskite films for high-efficiency solar cells. In this study, planar heterojunction (PHJ) CH3NH3PbI3 perovskite solar cells were prepared by the two-step spin-coating method. The uniformity of the perovskite light-absorbing layer is enhanced by air-assisted flow (AAF). We compared the photovoltaic performance characteristics of films prepared with and without AAF. Perovskite solar cells constructed without AAF showed a power conversion efficiency (PCE) of 8.67%, whereas a higher PCE of 13.28% was obtained with an AAF-based perovskite solar cell. Our study presents a useful technique for preparing high-quality perovskite films.

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Hygroscopic perovskite solar cells are commonly fabricated under conditions of inert atmosphere or low relative humidity (RH). To generate highperformance perovskite light-absorbing layers for super power conversion efficiency (PCE), we fabricated CH 3 NH 3 PbI 3 solar cells under ambient conditions (RH = 42-48%) by a flowing gas directly from high-RH air. The primary advantage of this technique, together with the casting of a hot solution and quick conduction, enabled us to achieve the highest and average PCEs of 16.32 and 14.27% respectively, with an extremely small deviation of 0.49%. Our research will be of significance for fabricating highly efficient and reproducible perovskite photovoltaics.