Self-Passivation of 2D Ruddlesden–Popper Perovskite by Polytypic Surface PbI2 Encapsulation

Two-dimensional Ruddlesden–Popper (2D RP) halide perovskites, C2MAn–1PbnI3n+1 (C = bulky ammonium cation; MA = methylammonium) with low n-members (n 2MA2Pb3I10 (n = 3) 2D RP induced by the electron beam. The surface dynamics reveal lateral growth of polytypic PbI2 with 3R, 4H, and 2H structures at the edge and surface of the 2D perovskite, accompanied by simultaneous annihilation at the other edges. Local radiolysis occurs dominantly by the internal energy increase of electron momentum transfer, which triggers a sequential layer-by-layer degradation into PbI2. In situ observation of the polytypic PbI2 growth at the whole surface and edges of 2D RP under electron irradiation elucidates how the outer PbI2 self-passivation can protect inner 2D RP, causing longer operando stability.