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A well-defined modulation reflection spectrum due to a multiple interference process is originated in the TiO 2 dye sensitizated solar cell (DSSC). Experimental evidence is shown that the interference process leading to the reflection spectrum takes place at the n-conducting F:SnO 2 (FTO) layer of the FTO/TiO 2 back contact. Moreover, the interference reflectance spectrum is influenced by the applied potential and illumination bias and disappears when FTO is metallized with 10 Å of platinum. These results show that FTO/TiO 2 cannot be considered as an ohmic but as a rectifying contact where the FTO behaves as a highly doped n-type semiconductor which absorbs an important part of the equilibrium contact potential in the dark. On the basis of our experimental results a new insight on the role of the dark equilibrium contact potential at the FTO/ TiO 2 interface in the processes of electric charge separation and photovoltage generation is given. Evidence is shown that the theoretically maximum attainable photovoltage in a DSSC is in one direction limited by the equilibrium redox potential in the dark, and in the other direction by the (light intensity dependent) bottom of the TiO 2 conduction band.

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 were less photostable with nanostructured ZnO compared to nanostructured . The best performance was confirmed for cis- on . However, it was 7–10 times less stable under other identical conditions on ZnO. Stability is favored by carboxylate anchoring and metal-centred electron transfer. In presence of , it is enhanced by formation of a stabilizing charge-transfer complex between oxidized Ru dye and back-bonding interfacial states. This is considered to be the main reason for the ongoing use of expensive Ru complexes in combination with . The local surface chemistry of the nanocrystalline turned out to be a crucial factor for sensitizer stability and requires further investigation.

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