Dresden 2026 – scientific programme

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O: Fachverband Oberflächenphysik

O 65: Solid-liquid interfaces: Reactions and electrochemistry II

O 65.1: Talk

Wednesday, March 11, 2026, 15:00–15:15, TRE/PHYS

Effect of Organic Additives in Aqueous Dye-Sensitized Solar Cells with TEMPO^+/0 Radicals as Redox Mediator Studied by Perturbation Techniques — •Daniel Holzhacker and Derck Schlettwein — Justus-Liebig-Universität Gießen, Institut für Angewandte Physik, Heinrich-Buff-Ring 16, D-35392 Gießen

Understanding the complex interactions among the electrolyte, dye, and semiconductor (TiO₂) in dye-sensitized solar cells (DSSCs) is crucial to uncover and optimize the individual roles of each component. Organic electrolyte additives, such as 1-methylbenzimidazole (1MBI), are commonly used to enhance cell performance. In aqueous TEMPO⁺ solutions, a distinctive color change was observed upon addition of 1MBI. Cyclic voltammetry revealed that the redox potential of the electrolyte shifted systematically to higher potentials with increasing 1MBI concentration. Photoelectrochemical analysis of DSSCs demonstrated a clear effect of 1MBI on the conduction band edge, which shifted in parallel to the redox potential of the electrolyte. It was shown that reduced recombination losses, i.e., a shift of the electron Fermi level in the TiO₂ closer to the conduction band edge, were responsible for an increased open-circuit voltage. Additionally, the shifts of both the conduction band edge and the redox level of the electrolyte may facilitate electron injection from the dye into TiO₂ and/or the regeneration of the oxidized dye by the redox mediator, thereby explaining the higher photocurrents, also observed at increased 1MBI concentrations.

Keywords: impedance spectroscopy; photoelectrochemistry; oxide electrodes; organic dye; water