Abstract
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 ∼ 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 σ*(CH3-NH3+: methylammonium cation) and σ*(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 MAPbI3 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.
Highlights
We report the presence of CH3NH2 neutral species on the surface and at grain boundaries in the interior of thin polycrystalline films of methylammonium lead iodide perovskite CH3NH3PbI3 that were prepared using a standard solution method
Two chemical states originated from CH3NH3þ and CH3NH2 in C 1s and N 1s corelevel spectra were observed using high-resolution x-ray photoelectron spectroscopy
We used the total electron yield (TEY) and partial electron yield (PEY) detection mode for NEXAFS spectra by recording the sample current normalized to a signal current, which was measured simultaneously using a gold mesh in ultrahigh vacuum (
Summary
We report the presence of CH3NH2 neutral species on the surface and at grain boundaries in the interior of thin polycrystalline films of methylammonium lead iodide perovskite CH3NH3PbI3 (thickness $ 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.
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