Research and progress of black metastable phase CsPbI3 solar cells

Recently, all-inorganic perovskite semiconductors have received widespread attention due to their excellent thermal stability. Among them, CsPbI3 with a suitable band gap (<1.73 eV) has achieved a power conversion efficiency (PCE) of more than 19%. However, at room temperature, its black phase easily turns into a yellow non-perovskite phase, which limits its commercial application. Particularly, among the three black phases, the cubic phase usually can be obtained at high temperature, and the preparation conditions are harsh, which limits its development in other regions. On the other hand, the metastable phases (beta, gamma phase) are relatively stable due to lower dissociation and formation energy, and lower phase transition temperature. Therefore, in this review, we mainly talk about the CsPbI3 perovskite solar cells (PSCs) based on the metastable phase. First, we introduce the crystal structure and electronic structure of the inorganic CsPbI3 perovskite. Then, the reasons for the thermodynamic instability of CsPbI3 are analyzed. Next, we focus on the latest progress in improving the performance and stability of CsPbI3 PSCs based on the metastable phase. Finally, the challenges and prospects for the future development of efficient and stable CsPbI3 perovskite solar cells are proposed.