The presence of CH3NH2 neutral species in organometal halide perovskite films

We report the presence of CH3NH2 neutral species not only on the surface but also at grain boundaries in the interior of thin polycrystalline films of methylammonium lead iodide perovskite CH3NH3PbI3 (thickness similar to 50 nm) that were prepared using a standard solution method. Different chemical states for C K-edge were observed at the surfaces and in the interiors of perovskite films. Salient features of sigma*(CH3-NH3+: methylammonium cation) and sigma*(CH3-NH2: methylamine neutral species) were observed at 290.3 and 292.8 eV in both partial (surface-sensitive) and total (bulk) electron yield modes by near-edge x-ray absorption fine structure measurements. Consistently, two chemical states originated from CH3NH3+ and CH3NH2 in C 1s and N 1s core-level spectra were observed using high-resolution x-ray photoelectron spectroscopy. Using density functional theory calculations, we show that CH3NH2 cannot reside stably in the MAPbI(3) perovskite crystal structure. Therefore, we propose that these CH3NH2 neutral species are mainly located on the surface or at grain boundaries in the interior of CH3NH3PbI3 films. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).