Unveiling the Effect of Cooling Rate on Grown‐in Defects Concentration in Polycrystalline Perovskite Films for Solar Cells with Improved Stability

Abstract Numerous efforts are devoted to reducing the defects at perovskite surface and/or grain boundary; however, the grown‐in defects inside grain is rarely studied. Here, the influence of cooling rate on the point defects concentration in polycrystalline perovskite film during heat treatment processing is investigated. With the combination of theoretical and experimental studies, this work reveals that the supersaturated point defects in perovskite films generate during the cooling process and its concentration improves as the cooling rate increases. The supersaturated point defects can be minimized through slowing the cooling rate. As a result, the optimized FAPbI 3 polycrystalline films achieve a superior carrier lifetime of up to 12.6 µs and improved stability. The champion device delivers a 25.47% PCE (certified 24.7%) and retain 90% of their initial value after >1100 h of operation at the maximum power point. These results provide a fundamental understanding of the mechanisms of grown‐in defects formation in polycrystalline perovskite film.