Turning Waste into Treasure: Pretreatment Strategy for Promoting Secondary Grain Growth by Reusing Excess Lead Iodide in Perovskite Solar Cells

Abstract Perovskite solar cells have witnessed remarkable progress in recent years, yet several pivotal factors persistently impede their widespread commercial adoption. Among these, the behavior of excess lead iodide (PbI 2 ) during perovskite synthesis is particularly concerning. Excess PbI 2 that promotes perovskite growth will accumulate at grain boundaries during annealing, which restricts the device performance and hinders its long‐term applicability. In this work, an innovative pretreatment strategy is developed by depositing the Cs 3 ErCl 6 quantum dots (QDs) on the perovskite film during annealing, which is different from the traditional post‐treatment strategy by depositing QDs after annealing. It is evident that PbI 2 can react with Cs 3 ErCl 6 QDs, enabling its secondary utilization and promoting the secondary growth of perovskite in the vicinity of grain boundaries to inhibit the formation of excess PbI 2 . The pretreated perovskite layer has a better fit grain, resulting in higher power conversion efficiency (PCE) and better stability of the device. The (FAPbI 3 ) 0.95 (MAPbBr 3 ) 0.05 perovskite solar cell treated using the pretreatment method demonstrates a champion PCE of 26.01%. This work offers new perspectives for inhibiting excessive PbI 2 growth and thus holds great promise for advancing the commercial viability of perovskite solar cells and contributing to the future landscape of renewable energy.