Taiyang Zhang¹ M. Ibrahim Dar² Ge Li¹ Feng Xu¹ Nanjie Guo¹ Michael Grätzel² Yixin Zhao¹

1, Shanghai Jiao Tong University, Shanghai, , China
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.