The optoelectronic properties improvement of double perovskites Cs₂SnI₆ by anionic doping (F^-)

Tin-based perovskite material is the best choice to replace heavy metal element lead during the last several years. Cs₂SnI₆ with Sn⁴⁺ is a fascinating optoelectronic material, which is a more air-stable composite cesium tin halide peroxide variant from CsSnI₃. However, the optoelectronic performance between N and P type of Cs₂SnI₆ varies considerably. Herein, we synthesized uniform Cs₂SnI₆ by modified two-step method, which thermal evaporated CsI firstly, and followed annealing in the SnI₄ and I₂ vapor at 150 °C resulted in uniform Cs₂SnI₆ films. SnF₄ is used as a dopant source to improve the optoelectronic properties of Cs₂SnI₆ films. Results indicate that good crystallinity was obtained for all films and the doped films underwent a crystalline plane meritocracy transition. The doped films had a flat, non-porous morphology with large grains. The high transmittance of the doped films in the infrared region led to the avoidance of self-generated thermal decomposition. With the help of F^-, the films became more conductive and had higher carrier mobility. DFT calculations showed that doping with F reduced the surface energy of (004), resulted in a preferred orientation transition in the crystal of Cs₂SnI₆. Fluorine doped double layer perovskite materials would have a broader application prospect.