Natural drying yields efficient perovskite solar cells

Natural drying (without spin coating or assistance of antisolvent, gas, or vacuum) might be the least-cost drying method to make perovskite films for solar cells. However, perovskite films made without quenching generally show undesirable morphology and low photovoltaic performance. In this work, we developed a high-throughput screening method to find the perovskite compositions that can form high-quality film without quenching process. We found that composition-graded perovskite films can be easily made by using a solution interdiffusion process, which produces perovskite films with continuously changing composition and the resulting film morphology, enabling fast screening of desired perovskite compositions. Several perovskites (CsPbI2Br, FA0.4Cs0.6PbI3, FA0.2MA0.8PbI3, and FA0.95Cs0.05PbI3) which can form high-quality films without quenching were successfully found. FA0.95Cs0.05PbI3 films yield a PCE of 23.28%, which is the highest PCE for perovskite solar cells with naturally-dried perovskite layer.