Low Temperature Fabrication for High Performance Flexible CsPbI₂Br Perovskite Solar Cells

All-inorganic CsPbX₃-based perovskites, such as CsPbI₂Br, show much better thermal and illumination stability than their organic-inorganic hybrid counterparts. However, fabrication of high-quality CsPbI₂Br 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 CsPbI₂Br 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 CsPbI₂Br 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 CsPbI₂Br solar cells fabricated at low temperature (120 °C). In addition, the method enables fabrication of flexible CsPbI₂Br 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 CsPbX₃-based perovskite solar cells (PSCs) at low temperature, particularly for flexible ones.