Role of Moisture and Oxygen in Defect Management and Orderly Oxidation Boosting Carbon‐Based CsPbI2Br Solar Cells to a New Record Efficiency

Abstract Large energy loss ( E loss ) caused by defect‐assisted recombination makes the photovoltaic performance of carbon‐based perovskite solar cells (C‐PSCs) inferior to that of metal‐electrode ones. Herein, the influence of environmental factors (moisture and oxygen) on defect management during re‐annealing process of CsPbI 2 Br crystalline films is systematically studied. Density functional theory and experimental results indicate that moisture in the air can significantly reduce the oxidation kinetics of crystalline films, resulting in orderly oxidation. Concomitantly, the oxidation decomposition products PbO and CsPbIBr 2 are enriched at grain boundaries, passivating surface defects efficiently. Simultaneously, energy band coupling between CsPbI 2 Br and CsPbIBr 2 improves the hole extraction efficiency. The photovoltage of corresponding C‐PSCs is increased from 1.05 to 1.32 V, indicating a reduced E loss derived from orderly oxidation strategy. Correspondingly, the champion cell achieves an efficiency of 15.27%, and a certified efficiency of 14.7%, which is a new record efficiency for CsPbI 2 Br C‐PSCs.