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 I-2 vapor at 150 degrees 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.