High Phase Stability in CsPbI Enabled by Pb-I Octahedra Anchors for Efficient Inorganic Perovskite Photovoltaics.

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