Phase Evolution in Methylammonium Tin Halide Perovskites with Variable Temperature Solid-State 119Sn NMR Spectroscopy

Abstract

Hybrid organic–inorganic metal-halide perovskite materials are an emerging class of materials that could profoundly change the optoelectronic and solar absorber research fields and have far-reaching applications. Unfortunately, the leading solar-absorbing candidates are lead-containing materials and suffer from chemical instability, eventually decomposing, resulting in detrimental long-term environmental concerns. A series of nontoxic group 14 Sn(II)-based hybrid organic–inorganic metal-halide perovskites is investigated using variable-temperature solid-state nuclear magnetic resonance (NMR) spectroscopy to examine their unique phases that appear between 150 and 540 K. Each phase of the MASnX3 (MA+ = CH3NH3+ and X– = Cl–, Br–, or I–) series is identified and compared to results from quantum chemical calculations of anionic polyhedron clusters. The analysis of the polyhedra about the Sn center is further related to the measured chemical shift anisotropy present when Sn deviates from octahedral symmetry. We also discuss the rapid degradation of pristine MASnI3 over 2 days studied using in situ 119Sn NMR spectroscopy. Finally, we report on the 1H, 13C, 119Sn, and 207Pb NMR structural properties of a Sn/Pb mixed B-site (MASn0.5Pb0.5I3) perovskite, demonstrating the sensitivity of the chemical shift to B-site substitution.