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  Dittrich, Th.; Neumann, B.; Tributsch, H.: Sensitization via reversibly inducible Ru(dcbpyH₂)₂(NCS)₂-TiO₂ charge transfer complex. The Journal of Physical Chemistry C 111 (2007), p. 2265-2269

10.1021/jp065830z

Abstract:
Abstract Charge separation has been investigated in pure and dyed (with N3 dye ¿ Ru(dcbpyH2)2(NCS)2) porous titania and ZnO by surface photovoltage spectroscopy. In atmospheres which do not contain oxygen or water, the onset of electron injection from adsorbed N3 dye molecules into titania shifts by 0.4 eV towards lower photon energies while the spectrum broadens. This reversible effect is apparently caused by the interaction of the adsorbed N3 dye molecules with Ti3+ states associated with oxygen vacancies and is interpreted to be the consequence of a long range charge transfer complex formation. No such effect is observed under identical conditions on ZnO, the Zn+ states of which cannot engage in d-backbonding. The possible consequences of this molecular interfacial property of TiO2 for the extraordinary activity and stability of the investigated Ru sensitizer in dye solar cells are discussed.