Interfacial Engineering by In Situ Building of a 3D/2D Heterojunction for Inverted CsPbI₂Br Solar Cells: Beyond Moisture Proof

In situ prepared 2D/3D hybrid heterojunction perovskites have attracted increasing interest in the field of photovoltaics due to their combined merits of 2D and 3D perovskites as well as approved applications in regular structured (n–i–p) perovskite solar cells (PSCs). Nevertheless, in situ building a 2D phase on 3D inorganic perovskites still remains challenging probably due to the resistance of the Cs+ ion toward the exchange reaction with most organic cations. In this work, we report the facile building of the 2D phase with n = 1 using highly conjugated benzimidazolium iodine (BIZI) instead of imidazolium iodine (IZI) for the posttreatment on a 3D CsPbI2Br absorber. The combined spectroscopic results reveal that the posttreatment and the as-formed 2D (BIZ)2PbI3Br result in not only moisture proof for the 3D CsPbI2Br absorber but also remarkable defect suppression/passivation and efficient hole blocking at the CsPbI2Br/PC61BM interface. As a result, the inverted (p–i–n) PSCs with an optimized 2D/3D structure deliver remarkably improved photovoltaic performance along with enhanced ambient stability compared to control devices. Thus, this study provides crucial information on how to in situ build a 2D/3D structure via ligand chemistry as well as how the 2D/3D structure influences the performance of inverted PSCs.