Regulating the crystalline phase of intermediate films enables FA1−xMAxPbI3 perovskite solar cells with efficiency over 22%

The sequential deposition method has achieved great success in the preparation of high-performance perovskite solar cells. Nevertheless, the crystalline phase of intermediate films which determines the quality of perovskite films and the corresponding device performance is yet to be fully understood. In this work, we show that FA1−xMAxPbI3 perovskite intermediate films prepared in ambient air are δ phase, which after annealing, present preferable orientation, higher crystallinity, longer photoluminescence carrier lifetime, and lower trap density than those obtained from α phase intermediate films. By integrating fully ambient-prepared perovskite films into planar heterojunction solar cells, a champion power conversion efficiency of 22.09% (steady-state efficiency of 21.03%) is achieved. Moreover, the unencapsulated device maintains 92.4% of its original efficiency after aging for 1200 h in ambient air (30 ± 5% relative humidity, 25 ± 5 °C, dark). This study provides new insight into preparation of high-quality perovskite films and solar cells.