Solvent-Coordinated Tin Halide Complexes as Purified Precursors for Tin-Based Perovskites

A series of solvent-coordinated tin halide complexes were prepared as impurity-free precursors for tin halide perovskites, and their structures were determined by single-crystal X-ray diffraction analysis. Using these precursors, the tin halide perovskites, MASnI(3) and FASnI(3), were prepared, and their electronic structures and photophysical properties were examined under inert conditions by means of photoelectron yield spectroscopy as well as absorption and fluorescence spectroscopies. Their valence bands (MASnI3: -5.02 eV; FASnI3: -5.16 eV) are significantly higher than those of MAPbI(3) or the typical hole-transporting materials 2,2', 7,7'-tetrakis(N, N-di-p-methoxyphenylamino)-9,9'-spirobifluorene and poly(bis(4-phenyl)(2,4,6-trimethylphenyl) amine). These results suggest that to develop the solar cells using these tin halide perovskites with efficient hole-collection properties, hole-transporting materials should be chosen that have the highest occupied molecular orbital levels higher than -5.0 eV.