Lead-tin halide perovskite thin films by chemical vapor deposition

Binary-metal halide perovskites films have attracted considerable attention, in an attempt to reduce the toxic lead (Pb) content in the perovskite thin films, while improving the charge transport properties without distorting the structure of the material. Chemical vapor deposition (CVD) has been successfully used to deposit Pb-only based perovskites with improved stability, but has limitation in controlling Sn-content when depositing Pb-Sn perovskites. We report on a two-step CVD method to synthesize methylammonium lead-tin triiodide perovskite films (MAPb_1-xSn_xI₃, x= 0 to 1), where the Sn-content, probed by Rutherford backscattering spectroscopy (RBS), is controlled. The perovskite films exhibit the characteristic tetragonal structure, independent of the Sn-loading. The inclusion of Sn in the structure has a direct influence on the optical properties of the films, manifested by the decrease in band gap from about 1.59 eV for MAPbI₃ to 1.26 eV for MAPb_0.4Sn_0.6I₃ and an increased defect density in the band gap that is associated with the increased oxidation of Sn²⁺ to Sn⁴⁺. In addition, we will report on the effect of the precursor material (SnI₂/PbI₂ and SnCl₂/PbCl₂) on the resultant structure and optical properties.