Mixed-halide Cs2SnI3Br3 perovskite as low resistance hole-transporting material in dye-sensitized solar cells

The crystal structure and physicochemical properties of the mixed-anion perovskite Cs2SnI3Br3 as well as its use as hole-transporting material in dye-sensitized solar cells have been investigated. The new airstable compound was prepared from the ternary perovskites Cs2SnBr6 and Cs2SnI6 in solid state and was characterized by powder X-ray diffraction analysis and Rietveld refinement. Raman and UV-vis spectroscopies were employed to determine the vibrational and optical characteristics both in bulk form and upon deposition on a TiO2 substrate. The effect of mixing Br and I atoms on the band structure and density of states was also evaluated with computational methods. The Cs2SnI3Br3 perovskite was successfully incorporated as hole-transporting material (HTM) in solid-state dye-sensitized solar cells (DSCs) based on mesoporous nanostructured titania electrodes sensitized with metal-organic (N719, Z907) and organic (MK2, D35) dyes, reaching a maximum power conversion efficiency of 3.63% with the Z907 dye, at 1 sun illumination. At 0.1 sun illumination, hole transport limitations are avoided and the efficiency is raised up to 7.3%. The electrochemical characteristics of the fabricated solar cells were also studied with impedance spectroscopy and reveal significantly lower charge-transport resistance for the perovskite compared to conventional HTMs. (C) 2015 Elsevier Ltd. All rights reserved.