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  Barkschat, A.; Moehl, T.; Macht, B.; Tributsch, H.: The function of TiO₂ with respect to sensitizer stability in nano-crystalline dye solar cells. International Journal of Photoenergy 2008 (2008), p. 814951/1-13

10.1155/2008/814951

Abstract:
Dyes of characteristically different composition have been tested with respect to long-term stability in operating standardized dye sensitized cells during a time period of up to 3600 hours. Selective solar illumination, the use of graded filters and imaging of photocurrents revealed that degradation is linked to the density of photocurrent passed. Photoelectrochemical degradation was observed with all sensitizers investigated. Sensitization was less efficient and sensitizers less photostable with nano-structured ZnO compared to nano-structured TiO2. The best performance was confirmed for cis RuII(dcbpyH2)2(NCS)2 on TiO2. However it was 7-10 times less stable under otherwise identical conditions on ZnO. Stability is favoured by carboxylate anchoring and metal centred electron transfer. In presence of TiO2 it is enhanced by formation of a stabilizing charge transfer complex between oxidised Ru dye and back-bonding interfacial Ti3+ states. This is considered to be the main reason for the ongoing use of expensive Ru-complexes in combination with TiO2.The local surface chemistry of the nano-crystalline TiO2 turned out to be a crucial factor for sensitizer stability and requires further investigation.