Potential Distribution and Photovoltage Origin in Nanostructured TiO2 Sensitization Solar Cells: An Interference Reflection Study

Abstract

A well-defined modulation reflection spectrum due to a multiple interference process is originated in the TiO2 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:SnO2(FTO) layer of the FTO/TiO2 back contact. Moreover, the interference reflectance spectrum is influenced by the applied potential and illumination bias and disappears when FTO is metallized with 10 A of platinum. These results show that FTO/TiO2 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/TiO2 interface in the processes of electric charge separation and photovoltage generation is given. Evidence is shown that the theoretically maximum attainable photovolta...