All-Inorganic Perovskite Solar Cells: Defect Regulation and Emerging Applications in Extreme Environments

All-inorganic perovskite solar cells (PSCs), such as CsPbX₃, have garnered considerable attention recently, as they exhibit superior thermodynamic and optoelectronic stabilities compared to the organic-inorganic hybrid PSCs. However, the power conversion efficiency (PCE) of CsPbX₃ PSCs is generally lower than that of organic-inorganic hybrid PSCs, as they contain higher defect densities at the interface and within the perovskite light-absorbing layers, resulting in higher non-radiative recombination and voltage loss. Consequently, defect regulation has been adopted as an important strategy to improve device performance and stability. This review aims to comprehensively summarize recent progresses on the defect regulation in CsPbX₃ PSCs, as well as their cutting-edge applications in extreme scenarios. The underlying fundamental mechanisms leading to the defect formation in the crystal structure of CsPbX₃ PSCs are firstly discussed, and an overview of literature-adopted defect regulation strategies in the context of interface, internal, and surface engineering is provided. Cutting-edge applications of CsPbX₃ PSCs in extreme environments such as outer space and underwater situations are highlighted. Finally, a summary and outlook are presented on future directions for achieving higher efficiencies and superior stability in CsPbX₃ PSCs.