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

Abstract CsPbI 3 inorganic perovskite has exhibited some special properties particularly crystal structure distortion and quantum confinement effect, yet the poor phase stability of CsPbI 3 severely hinders its applications. Herein, the nature of the photoactive CsPbI 3 phase transition from the perspective of PbI 6 octahedra is revealed. A facile method is also developed to stabilize the photoactive phase and to reduce the defect density of CsPbI 3 . CsPbI 3 is decorated with multifunctional 4‐aminobenzoic acid (ABA), and steric neostigmine bromide (NGBr) is subsequently used to further mediate the thin films' surface (NGBr‐CsPbI 3 (ABA)). The ABA or NG cation adsorbed onto the grain boundaries/surface of CsPbI 3 anchors the PbI 6 octahedra via increasing the energy barriers of octahedral rotation, which maintains the continuous array of corner‐sharing PbI 6 octahedra and kinetically stabilizes the photoactive phase CsPbI 3 . Moreover, the added ABA and NGBr not only interact with shallow‐ or deep‐level defects in CsPbI 3 to significantly reduce defect density, but also lead to improved energy‐level alignment at the interfaces between the CsPbI 3 and the charge transport layers. Finally, the champion NGBr‐CsPbI 3 (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.