Regulated Film Quality with Methylammonium Bromide Addition in a Two-Step Sequential Deposition to Improve the Performance of Perovskite Solar Cells

Generally, the quality of perovskite films, which includes surface coverage, grain size, crystallinity, and so forth, is the dominant factor to influence the performance of perovskite solar cells (PSCs). Here, we demonstrated a facile method to improve the film quality by adding different concentrations of methylammonium bromide (MABr) into the methylammonium iodide (MAI) solution in a two-step sequential deposition method. The optimized perovskite (MAPbI_3−xBr_x) film at a MAI/MABr (I/Br) weight ratio of 8:2 exhibits a significantly enhanced film quality with a uniform surface coverage on the substrate, high crystallinity, and few pinholes, which results in an increased UV/Vis absorption and photoluminescence emission. Finally, the associated PSC based on materials with an I/Br weight ratio of 8:2 displays an improved photovoltaic performance with a power conversion efficiency (PCE) of 15.03 % compared with the pristine MAPbI₃-based devices (PCE=11.39 %). In conclusion, this work demonstrates an effective and facile strategy to enhance the perovskite film quality.