Combined experimental and theoretical investigation of optical, structural, and electronic properties ofCH3NH3SnX3thin films(X=Cl,Br)

Well-oriented thin films of methyl-ammonium trihalogenostannates $\mathrm{C}{\mathrm{H}}_{3}\mathrm{N}{\mathrm{H}}_{3}\mathrm{Sn}{X}_{3}$ compounds $(X=\mathrm{Cl},\mathrm{Br})$ are grown by the single source thermal ablation technique. Optical absorption and structural analysis of $\mathrm{C}{\mathrm{H}}_{3}\mathrm{N}{\mathrm{H}}_{3}\mathrm{Sn}{X}_{3}$ thin films are combined with ab initio calculations in order to clarify their electronic properties and the role of the organic cation. The structural calculations reproduce well the measured lattice parameters, and optical measurements reveal a direct gap absorption onset for both compounds, in agreement with the calculated band structures. It turns out from projected density of states analysis that the valence and conduction bands take negligible contribution from the methylammonium. It is inferred that the band gap mainly depends on the ionicity and size of the inorganic cage $\mathrm{Sn}{X}_{3}$.