Dye-sensitised solar cells based on metal complexes with pendant catecholate anchoring groups

Metal complexes which absorb light strongly can be used as the basis of solar cells. By attachment of these metal complexes to the surface of a semiconductor such as titanium dioxide, light can be convertedsto electricity; the energy of the light absorbed by each molecule results in injection of an electron into the semiconductor which results in a current flow.The effectiveness of these depends on several factors, especially (i) how strongly the molecules bind to the TiO2 surface, and (ii) prevention of back electron-transfer, where the injected electron recombines with the dye molecule rather than generating an electric current. This project aims to address both of these areas. We have already shown that metal complexes with a catechol (1,2-dihydroxybenzene) group attached to the periphery attach exceptoinally strongly to the TiO2 surface, and we plan to make additional complexes along these lines to investogate their performance as sensitisers (generators of electric current) in solar cells. The problem of undesired back electron-transfer will be addressed by also attaching amine groups to the periphery of the complexes, which will (quickly) donate an electron to fill the gap left after charge injection, thereby preventing back electron-tramsfer from the TiO2 to the metal complex.We will prepare several new complexes along these lines, carry out a detailed study of their photophysical and electrochemical properties, and then determine how well they perform in prototypical solar cell devices. It is hoped that the new complexes will provide better long-term performance than existing systems because of their very tight binding to the TiO2 surface.