Ab initioinvestigation of hybrid organic-inorganic perovskites based on tin halides

The structural and electronic properties of both inorganic and hybrid organic-inorganic perovskites based on tin halides are investigated from the first principles. In particular, we contrast the inorganic ${\text{CsSnCl}}_{3}$ and ${\text{CsSnI}}_{3}$ to their hybrid counterparts $({\text{CH}}_{3}{\text{NH}}_{3}){\text{SnCl}}_{3}$, $({\text{CH}}_{3}{\text{NH}}_{3}){\text{SnI}}_{3}$, and $({\text{NH}}_{2}\text{CH}={\text{NH}}_{2}){\text{SnI}}_{3}$, which were obtained by substituting the inorganic Cs cation with the methylammonium ${\text{CH}}_{3}{\text{NH}}_{3}$ and the formamidinium ${\text{NH}}_{2}\text{CH}={\text{NH}}_{2}$ cations. The comparison between the hybrid perovskites and the inorganic counterparts sheds light on the effects of the filling molecule on the structural and electronic properties of the compound. We show that the stability against the distortion of the perovskitic cage strongly depends on the embedded cation. The electronic properties (in particular, the band gap) can be tuned by a suitable choice of the organic molecule, and, in particular, of its size.