Chemically Stable Black Phase CsPbI 3 Inorganic Perovskites for High‐Efficiency Photovoltaics

Research on chemically stable inorganic perovskites has achieved rapid progress in terms of high efficiency exceeding 19% and high thermal stabilities, making it one of the most promising candidates for thermodynamically stable and high‐efficiency perovskite solar cells. Among those inorganic perovskites, CsPbI 3 with good chemical components stability possesses the suitable bandgap (≈1.7 eV) for single‐junction and tandem solar cells. Comparing to the anisotropic organic cations, the isotropic cesium cation without hydrogen bond and cation orientation renders CsPbI 3 exhibit unique optoelectronic properties. However, the unideal tolerance factor of CsPbI 3 induces the challenges of different crystal phase competition and room temperature phase stability. Herein, the latest important developments regarding understanding of the crystal structure and phase of CsPbI 3 perovskite are presented. The development of various solution chemistry approaches for depositing high‐quality phase‐pure CsPbI 3 perovskite is summarized. Furthermore, some important phase stabilization strategies for black phase CsPbI 3 are discussed. The latest experimental and theoretical studies on the fundamental physical properties of photoactive phase CsPbI 3 have deepened the understanding of inorganic perovskites. The future development and research directions toward achieving highly stable CsPbI 3 materials will further advance inorganic perovskite for highly stable and efficient photovoltaics.