Interface Modification for Efficient and Stable Inverted Inorganic Perovskite Solar Cells

Due to their excellent thermal stability and ideal bandgap, metal halide inorganic perovskite based solar cells (PSCs) with inverted structure are considered as an excellent choice for perovskite/silicon tandem solar cells. However, the power conversion efficiency (PCE) of inverted inorganic perovskite solar cells (PSCs) still lags far behind that of conventional n–i–p PSCs due to interfacial energy level mismatch and high nonradiative charge recombination. Herein, the performance of inverted PSCs is significantly improved by interfacial engineering of CsPbI3−xBrx films with 2‐mercapto‐1‐methylimidazole (MMI). It is found that the mercapto group can preferably react with the undercoordinated Pb2+ from perovskite by forming Pb–S bonds, which appreciably reduces the surface trap density. Moreover, MMI modification results in a better energy level alignment with the electron‐transporting material, promoting carrier transfer and reducing voltage deficit. The above combination results in an open‐circuit voltage enhancement by 120 mV, yielding a champion PCE of 20.6% for 0.09 cm2 area and 17.3% for 1 cm2 area. Furthermore, the ambient, operational and heat stabilities of inorganic PSCs with MMI modification are also greatly improved. The work demonstrates a simple but effective approach for fabricating highly efficient and stable inverted inorganic PSCs. The formation of Pb–S bonds between perovskite and 2‐mercapto‐1‐methylimidazole appreciably reduces surface trap and improves interfacial energy level alignment. The open circuit voltage of inverted inorganic perovskite solar cells is enhanced by 120 mV, yielding a power conversion efficiency of 20.6%, along with improved ambient stability.