The influence of fluoroalkyl chains in redox electrolytes for energy conversion

We discovered an unprecedented fundamental interaction originated from the fluoroalkyl chains at the interface between light harvesting chromophore and charge transport redox electrolyte in dye-sensitized solar cells (DSSCs). A fluoroalkylated Ru complexes dye (FN719) was synthesized and upon anchoring on nanoparticulate TiO₂ electrodes, FN719 exhibits 5 times better photostability in humid air than that of the conventional N719 due to the hydrophobicity of the fluoroalkyl chains. Moreover, the lipophobicity of fluoroalkylated chains in organic electrolyte causes a size-selective steric hindrance with respect to the redox couple I^-/I₃^-, leading to a more stalled diffusion of the bulky I₃^- towards dyes and TiO₂ photoanode than that of the lean I^-. As such, without sacrificing the forward electron transport and quantum efficiency, the recombination in FN719-based DSSCs is suppressed to be 1.3 times slower than N719-based DSSCs studied by the photovoltage transients and electrochemical impedance spectroscopy; and the adverse I₃^- exchange with SCN^- on dye is also inhibited as manifested by mass spectrometry. The J-V measurements suggest improved efficiency in FN719-based cells (9.2%) than similarly fabricated N719-based cells (8.5%).