2D Capping Layer Passivation toward Inorganic CsPbI₃ Perovskite Minimodule

Abstract Surface termination is so far the mainstream passivating method to enhance the performance of CsPbI₃ solar cells. However, surface termination can hardly achieve effective and homogeneous passivation on large‐area CsPbI₃ films, which is one key challenge toward high‐performance inorganic perovskite solar modules (PSMs). The strong ionic bond between Cs and the Pb‐I framework in inorganic CsPbI₃ makes it difficult to construct 2D perovskite layer on film surface via post treatment, which is otherwise a classic and effectual approach for defect elimination in organic–inorganic hybrid perovskites. Herein, a novel and programmable surface reconstruction strategy is reported that can facilely tune surface termination to 2D passivation on CsPbI₃ perovskite using 2‐(1‐cyclohexenyl) ethyl ammonium iodide (CHEAI). In comparison to surface termination, the in situ formation of 2D CHEA₂PbI₄ by adjusting the stoichiometry of CHEAI demonstrates more comprehensive passivation effects and favorable energy level alignment for CsPbI₃ films. Such 2D construction has greatly facilitated the enhancement on device performance, especially when scaling up the area. The optimal CsPbI₃ PSM (active area of 12.44 cm²) based on 2D CHEA₂PbI₄ achieves a record‐high efficiency of 19.32% (certified efficiency of 18.83%) with much improved stability, endorsing the practical promotion of this intrinsically stable perovskite material.