High Phase Stability in CsPbI₃ Enabled by Pb–I Octahedra Anchors for Efficient Inorganic Perovskite Photovoltaics

Abstract CsPbI₃ inorganic perovskite has exhibited some special properties particularly crystal structure distortion and quantum confinement effect, yet the poor phase stability of CsPbI₃ severely hinders its applications. Herein, the nature of the photoactive CsPbI₃ phase transition from the perspective of PbI₆ octahedra is revealed. A facile method is also developed to stabilize the photoactive phase and to reduce the defect density of CsPbI₃. CsPbI₃ is decorated with multifunctional 4‐aminobenzoic acid (ABA), and steric neostigmine bromide (NGBr) is subsequently used to further mediate the thin films' surface (NGBr‐CsPbI₃(ABA)). The ABA or NG cation adsorbed onto the grain boundaries/surface of CsPbI₃ anchors the PbI₆ octahedra via increasing the energy barriers of octahedral rotation, which maintains the continuous array of corner‐sharing PbI₆ octahedra and kinetically stabilizes the photoactive phase CsPbI₃. Moreover, the added ABA and NGBr not only interact with shallow‐ or deep‐level defects in CsPbI₃ to significantly reduce defect density, but also lead to improved energy‐level alignment at the interfaces between the CsPbI₃ and the charge transport layers. Finally, the champion NGBr‐CsPbI₃(ABA)‐based inorganic perovskite solar cell delivers 18.27% efficiency with excellent stability. Overall, this work demonstrates a promising concept to achieve highly phase‐stabilized inorganic perovskite with suppressed defect density for promoting its optoelectronic applications.