Dynamic Surface Reconstruction of 2D Ruddlesden-Popper Halide Perovskite under e-Beam Irradiation

Abstract

Two-dimensional (2D) Ruddlesden-Popper (RP) halide perovskites, C2MAn-1PbnI3n+1 (C=bulky ammonium cation; MA=methyl-ammonium) with low n (n<5), have been gathering an broad attention in solar cell or optoelectronic application due to not only long term stability under oxygen environment but also unique optoelectronic property such as bandgap tunability by thickness control of quantum well (QW) halide perovskite and sharp absorption edges in the visible range against 3D halide perovskite (n=∞) such as MAPbI3 [1][2][3][4][5],where MA is methyl-ammonium (CH3NH3 + ). A BA2MA2Pb3I10 is one species (n=3 type) of the 2D-RP perovskites and has repeating sequence of three monolayers of semiconducting hybrid organic-inorganic MA2Pb3I10 perovskites and QW barrier insulating molecules, which are butyl-ammonium molecules (BA, CH3(CH2)3NH3 + ) separating the semiconducting layers as can be seen in Fig. 1. While the electron beam irradiation effect on the 3D halide perovskite materials have been investigated [5][6][7][8][9], studies on 2D halide perovskites are lacking.Herein we present dynamic surface modification on a BA2MA2Pb3I10 (n=3) 2D perovskite with BA (butyl-ammonium, CH3(CH2)3NH3+) working as QW barrier molecules induced by electron beam in transmission electron microscope. We observed various surface dynamics in atomic level under electron irradiation such as lateral growth in c planes of polytypic PbI2 with 3R, 4H and 2H structures at the edge surface of the 2D perovskite accompanied with simultaneous annihilation of surface plane as can be seen in Fig. 1 and 2. Furthermore, we observe newly reconstructed regions generated by long electron irradiation which are confirmed to be PbI2, driven by local radiolysis due to internal energy increase of electron momentum transfer rather than knock-on damage mechanism. Moiré fringe from PbI2 formation on the BA2MA2Pb3I10 is also observed. Direct observation on the atomically reconstructed surface of the 2D halide perovskite driven by increased internal energy will provide insight of stability under total dose level of e-beam irradiation in TEM.[1] C. C. Stoumpos et al