Suppressing Oxidation at Perovskite–NiO_x Interface for Efficient and Stable Tin Perovskite Solar Cells

Abstract Inorganic nickel oxide (NiO_x) is an ideal hole transport material (HTM) for the fabrication of high‐efficiency, stable, and large‐area perovskite photovoltaic devices because of its low cost, stability, and ease of solution processing. However, it delivers low power conversion efficiency (PCE) in tin perovskite solar cells (TPSCs) compared to other organic HTMs. Here, the origin of hole transport barriers at the perovskite–NiO_x interface is identified and a self‐assembled monolayer interface modification is developed, through introducing (4‐(7H‐dibenzo[c,g]carbazol‐7‐yl)ethyl)phosphonic acid (2PADBC) into the perovskite–NiO_x interface. The 2PADBC anchors undercoordinated Ni cations through phosphonic acid groups, suppressing the reaction of highly active Ni^≥3+ defects with perovskites, while increasing the electron density and oxidation activation energy of Sn at the perovskite interface, reducing the interface nonradiative recombination caused by tetravalent Sn defects. The devices deliver significantly increased open‐circuit voltage from 0.712 to 0.825 V, boosting the PCE to 14.19% for the small‐area device and 12.05% for the large‐area (1 cm²) device. In addition, the 2PADBC modification enhances the operational stability of NiO_x‐based TPSCs, maintaining more than 93% of their initial efficiency after 1000 h.