Low Temperature Fabrication for High Performance Flexible CsPbI(2)Br Perovskite Solar Cells

All‐inorganic CsPbX(3)‐based perovskites, such as CsPbI(2)Br, show much better thermal and illumination stability than their organic–inorganic hybrid counterparts. However, fabrication of high‐quality CsPbI(2)Br perovskite film normally requires annealing at a high temperature (>250 °C) that is not compatible with the plastic substrate. In this work, a Lewis base adduct‐promoted growth process that makes it possible to fabricate high quality CsPbI(2)Br perovskite films at low temperature is promoted. The mechanism is attributed to synthesized dimethyl sulfoxide (DMSO) adducts which allow a low activation energy route to form CsPbI(2)Br perovskite films during the thermal annealing treatment. A power conversion efficiency (PCE) of 13.54% is achieved. As far as it is known, this is the highest efficiency for the CsPbI(2)Br solar cells fabricated at low temperature (120 °C). In addition, the method enables fabrication of flexible CsPbI(2)Br PSCs with PCE as high as 11.73%. Surprisingly, the bare devices without any encapsulation maintain 70% of their original PCEs after being stored in ambient air for 700 h. This work provides an approach for preparing other high performance CsPbX(3)‐based perovskite solar cells (PSCs) at low temperature, particularly for flexible ones.