Synthesis, characterization of ((CH3)3S)2SnI6-nCln and ((CH3)3S)2SnI6-nBrn (n=1, 2) perovskites and use in dye-sensitized solar cells

摘要： New air-stable ((CH3)3S)2SnI6-nCln and ((CH3)3S)2SnI6-nBrn (n=1, 2) defect perovskites were synthesized and their physicochemical properties were established. Rietveld analysis on the recorded XRD patterns revealed the presence of cubic structural modification with a 0D network of [SnI6-nCln] and [SnI6-nBrn] octahedra. The vibrational and electronic properties of the mixed-anion based trimethylsulfoinum Tin (IV) perovskites investigated using Raman and UV–vis spectroscopy showed that upon substitution of Cl/Br for I, the electronic band gap slightly increased, while the lattice vibrations were also largely affected. Density functional theory (DFT) calculations permitted to determine the density of states (DOS) distribution and corresponding band energy structures, confirming the obtained increase of direct band gap values with halogen substitution. The lead-free Sn(IV)-based compounds were successfully incorporated as hole transporting materials (HTMs) in sensitized nanocrystalline solar cells (DSCs). For these devices, power conversion efficiencies as high as 5% were obtained, under 1 sun (A.M. 1.5G) illumination. Electrochemical impedance spectroscopic analysis indicated that the maximum device performance is associated with high charge recombination resistance and low electron transfer resistance at dye/perovskite and perovskite/Pt interfaces, respectively.