2, École Polytechnique Fédérale de Lausanne, Lausanne, , Switzerland
Among various all-inorganic halide perovskites exhibiting better thermo stability than organic-inorganic halide perovskites, α-CsPbI3 with the most suitable band gap for tandem solar cell application suffers an issue of phase instability under ambient conditions. We discovered that a small amount of two-dimensional (2D) EDAPbI4 perovskite containing the bication ethylenediamine (EDA) could stabilize the α-CsPbI3 thus avoid the undesirable formation of the nonperovskite δ phase. Moreover, not only the 2D perovskite of EDAPbI4 facilitate the formation of α-CsPbI3perovskite films exhibiting high phase stability at room temperature for months and at 100°C for >150 hours but also the α-CsPbI3 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.