2D Capping Layer Passivation toward Inorganic CsPbI3 Perovskite Minimodule

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.