| People involved: | Villy Sundström, Arkady Yartsev |
| Former members: | Sophie Canton, Mathias Pellnor, Gabor Benkö, Arunkumar Kathiravan |
This project is related to the following Fields, Subjects and Techniques:
| Fields: | Ultrafast Chemistry, Physics and Biology, Photochemistry and Photophysics, Surfaces and Interfaces |
| Subjects: | Dye-sensitized Solar Cells, Nanostructures |
| Techniques: | Pump-probe spectroscopy |
Dye-sensitized semiconductor systems were recently introduced as alternatives to conventional semiconductor materials in solar cells. Additional applications are in photocatalysis, sensors etc. A thin film of a nanostructured wide band gap semiconductor (only absorbing uv-light), typically TiO2, SnO2, or ZnO, sensitised to visible light by an organic dye molecule or other sensitizer is the key component of the system. Light absorption by the sensitizer initiates electron transfer from the sensitizer to the semiconductor, where free electrons can be harvested as current (solar cell), used for redox actions (catalysis), or constitutes an electrical impulse (sensor). Despite a significant body of research during the last 15 years an understanding of the relation between fundamental processes and conversion efficiency/performance of the solar cell is not at hand. It still remains as a great challenge to understand how light absorption, charge generation, recombination and transport, as well as processes involving the redox mediator contribute to the overall performance of the solar cell.
For highest efficiency of a solar cell, the quantum efficiency of charge injection into the semiconductor should be high, charge recombination between oxidized dye and conduction band electrons slow as compared to re-reduction of the dye by the redox couple, see Fig. 1. The sensitizer molecule plays a very important role in controlling these processes, as the component by which the efficiency of light harvesting and communication of the light energy to the charge-carrying semiconductor is determined. Factors such as spectral coverage of the sensitizer, sensitizer-semiconductor binding (and thus electronic coupling), sensitizer aggregation, driving force of electron injection, rate of charge recombination, is expected to be sensitive to the choice of sensitizer. In addition, for large scale production of solar cells it is essential that the sensitizer complies with requirements of environmental friendly production and recycling.
In order to examine the factors that control function of an efficient sensitizer we are exploring the interfacial electron transfer processes of different types of sensitizers, polypyridyl-transition metal complexes (e.g. RuN3), porphyrins, all-organic sensitizers. Several types of sensitizers are illustrated in the figure.
