Formation of Low-Dimensional Double Perovskite Layers by ABS and PEAI Sequential Treatment for Achieving High-Performance CsPbI3 Solar Cells

All-inorganic CsPbI3 perovskite has emerged as an alternative photovoltaic material owing to its good thermal stability and ideal bandgap for tandem applications. However, CsPbI3 perovskite solar cells (PSCs) still show poor phase stability and low efficiency. Herein, we propose a new strategy to form low-dimensional double perovskite (2D-PEA2PbI4 and quasi-2D-PEA2(CsPbI3)PbI4) layers on the CsPbI3 film by sequential treatment with ammonium benzenesulfonate (ABS) and phenylethylammonium iodide (PEAI). After ABS treatment, additional PbI2 was in situ formed on the CsPbI3 film surface, which further reacted with PEAI to generate low-dimensional double perovskite layers. The low-dimensional double perovskite layers effectively enhanced the efficiency and stability of CsPbI3 solar cells. Consequently, a power conversion efficiency (PCE) of 19.06% is achieved. The unencapsulated device retained approximately 70% of its initial PCE after aging 300 h under ambient conditions. This study provides a new approach for the application of low-dimensional perovskites in all-inorganic PSCs.