Combined experimental and theoretical investigation of optical, structural, and electronic properties of CH$_3$NH$_3$Sn$X_3$ thin films ($X$=Cl,Br)
Fabio Chiarella, Andrea Zappettini, Francesca Licci, Ivo Borriello, Giovanni Cantele, Domenico Ninno, Antonio Cassinese, and Ruggero Vaglio

Well-oriented thin films of methyl-ammonium trihalogenostannates \snx compounds (X = Cl, Br) are grown by the single source thermal ablation technique. Optical absorption and structural analysis of \snx thin films are combined with \textit{ab-initio} calculations in order to clarify their electronic properties and the role of the organic cation. The structural calculations well reproduce the measured lattice parameters and optical measurements reveal a direct gap absorption onset for both compounds, in agreement with the calculated band structures. From projected density of states (PDOS) analysis turns out that the valence and conduction band take negligible contribution from the methylammonium. It is inferred that the band gap mainly depends on the ionicity and size of the inorganic cage SnX$_3$.

© 2008 The American Physical Society.