Ruthenium bis-terpyridine complexes connected to an oligothiophene unit for dry dye-sensitised solar cells

The preparation of a series of new heteroleptic ruthenium complexes containing a 4'-phosphonic acid terpyridine and a terpyridine substituted in 4' position by a bithiophene or tert-thiophene are described. The UV-Vis absorption and emission spectra along the redox potentials of these complexes are reported. These new complexes were also tested as sensitizers in dry dye-sensitised solar cell using regioregular polyoctylthiophene as a solid hole conductor. It has been shown that the complexes substituted with thiophene chain exhibit poor photovoltaic efficiency most probably due to low electron injection efficiency. This latter property can be rationalised by the fact that the LUMO orbitals in these complexes are localised in the terpyridine substituted by the thiophene chain and not in the terpyridine phosphonic which is bonded to the TiO2 photoanode.