Fast cascade neutralization of an oxidized sensitizer by an in situ-generated ionic layer of I− species on a nanocrystalline TiO2 electrode

Abstract

We report a novel way to accelerate the rate of oxidized sensitizer neutralization on nanocrystalline TiO₂ electrode surfaces using a novel coadsorbent, 3,4,5-tris-butenyloxy benzoic acid (TD), having three terminal double bonds. ¹H NMR and contact angle measurements revealed that the terminal double bonds reacted with I₂ to form an in situ-generated ionic layer of I⁻ species. Transient absorption spectroscopy (TAS) and electrochemical impedance spectroscopy (EIS) studies demonstrated that I⁻ species neighbouring the cationic dye molecules (D⁺) accelerate the neutralization (or regeneration) rate (k_D⁺), as well as decrease the recombination reactions of photoinduced electrons with D⁺ (k₁) and I₃⁻ (k₂). Dye-sensitized solar cells treated with TD exhibit a power conversion efficiency of 10.2%, which is 22% higher due to the simultaneous improvements in J_SC and V_OC, even at 15% low dye loading levels, compared to the values obtained from a conventional device.