Precursor Engineering for All‐Inorganic CsPbI₂Br Perovskite Solar Cells with 14.78% Efficiency

The optoelectronic properties of perovskite films are closely related to the film quality, so depositing dense, uniform, and stable perovskite films is crucial for fabricating high‐performance perovskite solar cells (PSCs). CsPbI 2 Br perovskite, prized for its superb stability toward light soaking and thermal aging, has received a great deal of attention recently. However, the air instability and poor performance of CsPbI 2 Br PSCs are hindering its further progress. Here, an approach is reported for depositing high‐quality CsPbI 2 Br films via the Lewis base adducts PbI 2 (DMSO) and PbBr 2 (DMSO) as precursors to slow the crystallization of the perovskite film. This process produces CsPbI 2 Br films with large‐scale crystalline grains, flat surfaces, low defects, and long carrier lifetimes. More interestingly, PbI 2 (DMSO) and PbBr 2 (DMSO) adducts could significantly improve the stability of CsPbI 2 Br films in air. Using films prepared by this technique, a power conversion efficiency (PCE) of 14.78% is obtained in CsPbI 2 Br PSCs, which is the highest PCE value reported for CsPbI 2 Br‐based PSCs to date. In addition, the PSCs based on DMSO adducts show an extended operational lifetime in air. These excellent performances indicate that preparing high‐quality inorganic perovskite films by using DMSO adducts will be a potential method for improving the performance of other inorganic PSCs.