Iron Redox Shuttles with Wide Optical Gap Dyes for High-Voltage Dye-Sensitized Solar Cells

A series of iron polypyridyl redox shuttles were synthesized in the 2+ and 3+ oxidation states and paired with a series of wide optical gap organic dyes with weak aryl ether electron-donating groups. High voltage dye-sensitized solar cell (HV-DSC) devices were obtained through controlling the redox shuttle energetics and dye donor structure. The use of aryl ether donor groups, in place of commonly used aryl amines, allowed for the lowering of the dye ground-state oxidation potential which enabled challenging to oxidize redox shuttles based on Fe²⁺ polypyridyl structures to be used in functional devices. By carefully designing a dye series that varies the number of alkyl chains for TiO₂ surface protection, the recombination of electrons in TiO₂ to the oxidized redox shuttle could be controlled, leading to HV-DSC devices of up to 1.4 V.