Photovoltaics of low-bandgap inorganic perovskites

Low-bandgap inorganic perovskites are a group of materials that can simultaneously harness the stability merit of an all-inorganic composition and high photovoltaic efficiency potential of low-bandgap light absorbers as compared with other perovskite materials. Therefore, low-bandgap inorganic perovskites are promising materials options for the development of both single-junction and tandem solar cells. In this review, we summarize the recent studies addressing the major issues related to these perovskites, including the low phase stability and uncontrolled Sn-related defects. We also present a perspective discussion on future research directions related to these perovskites. We propose to gain insights into those unique thermodynamic and kinetic behaviors of these perovskites to understand and overcome their low phase stability. In particular, we envision that fundamental investigations leveraging ¹¹⁹Sn NMR may open a new pathway for understanding and alleviating Sn-related defects. Continued efforts in the discussed areas are expected to unleash the full technological potential of low-bandgap inorganic perovskites for high-performance solar cells and modules.