Bication lead iodide 2D perovskite component to stabilize inorganic α-CsPbI perovskite phase for high-efficiency solar cells.

Among various all-inorganic halide perovskites exhibiting better stability than organic-inorganic halide perovskites, α-CsPbI with the most suitable band gap for tandem solar cell application faces an issue of phase instability under ambient conditions. We discovered that a small amount of two-dimensional (2D) EDAPbI perovskite containing the ethylenediamine (EDA) cation stabilizes the α-CsPbI to avoid the undesirable formation of the nonperovskite δ phase. Moreover, not only the 2D perovskite of EDAPbI facilitate the formation of α-CsPbI perovskite films exhibiting high phase stability at room temperature for months and at 100°C for >150 hours but also the α-CsPbI perovskite solar cells (PSCs) display highly reproducible efficiency of 11.8%, a record for all-inorganic lead halide PSCs. Therefore, using the bication EDA presents a novel and promising strategy to design all-inorganic lead halide PSCs with high performance and reliability.