Ordered Mesoporous Tungsten Suboxide Counter Electrode for Highly Efficient Iodine-Free Electrolyte-Based Dye-Sensitized Solar Cells

A disulfide/thiolate (T2/T−) redox‐couple electrolyte, which is a promising iodine‐free electrolyte owing to its transparent and noncorrosive properties, requires alternative counter‐electrode materials because conventional Pt shows poor catalytic activity in such an electrolyte. Herein, ordered mesoporous tungsten suboxide (m‐WO3−x), synthesized by using KIT‐6 silica as a hard template followed by a partial reduction, is used as a catalyst for a counter electrode in T2/T−‐electrolyte‐based dye‐sensitized solar cells (DSCs). The mesoporous tungsten suboxide, which possesses interconnected pores of 4 and 20 nm, provides a large surface area and efficient electrolyte penetration into the m‐WO3−x pores. In addition to the advantages conferred by the mesoporous structure, partial reduction of tungsten oxide creates oxygen vacancies that can function as active catalytic sites, which causes a high electrical conductivity because of intervalence charge transfer between the W5+ and W6+ ions. m‐WO3−x shows a superior photovoltaic performance (79 % improvement in the power conversion efficiency) over Pt in the T2/T− electrolyte. The superior catalytic activity of m‐WO3−x is investigated by using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization curve analysis. WOx before Pt: Ordered mesoporous tungsten suboxide (m‐WO3−x) is synthesized by using a hard template and a partial reduction process. The m‐WO3−x is used as an alternative catalyst for a counter electrode (CE) instead of Pt for iodine‐free electrolyte (T2/T−)‐based dye‐sensitized solar cells. The catalytic activity of m‐WO3−x CE is superior to that of conventional Pt CEs.