Project Details
Projekt
Mechanistic analysis of dye regeneration and recombination processes at dye-sensitized solar cells using microelectrochemical experiments
Subject Area
Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
Term
from 2015 to 2019
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 260064828
Dye-sensitized solar cells (DSCs) based on ZnO as semiconductor allow the fabrication of flexible solar cells that are capable of delivering electrical energy even under diffuse illumination and that can be produced from abundant materials. In these cells, the light is absorbed by a dye that injects an electron into the conduction band of the semiconductor. For a continuous operation, the photo-oxidized dye must be reduced by, e.g., a redox-active component of the electrolyte. The aim of this research project is the investigation of the kinetics of this dye regeneration process because it can, together with recombination processes, limit the performance of such cells. A direct experimental access to such data presently does not exist although it is highly desirable to understand and subsequently optimize the dependence of the regeneration kinetics on electrolyte components (solvent, redox electrolyte, additives) and electrode structures. Because of the complex interdependencies, the optimization of a particular cell component typically requires the alteration of other components, a task presently to be performed largely empirically because characterization techniques are still missing that can assess individual process steps under realistic conditions. The new characterization scheme will be developed exemplarily on cells based on nanostructured, electrodeposited ZnO. The results will be compared to established DSC based on nanoparticular TiO2 or ZnO with adjustable morphologies of the porous photoanodes. We follow the hypothesis that internal mass transport limitations have an effect on the overall performance and that this adverse effect can be limited by establishing additional charge transport processes at the inner surfaces of the materials. In addition, the chemically more reactive surface of ZnO requires different dyes than TiO2. New electrolytes with more favorable redox potentials in principle allow higher efficiencies. However, they pose higher demand on the quality of layers that block electron transfer from the contacts to avoid loosing the gained efficiencies through accelerated recombination processes. The proposed methodology is based on a combination of classical procedures for the characterization of DSC performance, impedance spectroscopy in the dark and under illumination, experiments under modulated light intensity as well as microelectrochemical methods on the basis of scanning electrochemical microscopy (SECM), which will be further developed by use of transient signals, the use of sealed microelectrochemical cells or DSC with very restricted openings. If the hypothesis and the developed methodology can be confirmed, they will guide the selection and adaptation of new dyes, new redox electrolytes and new solvent systems to photoanodes with optimized blocking layers.
DFG Programme
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