Thermal Processing and Characterizations of Dye-Sensitized Solar Cells Based on Nanostructured TiO2

This work reports an extensive study about the effects of thermal treatments on the performance of TiO2-based dye-sensitized solar cells. The morphologic, structural, luminescence, and electrical properties of the as-prepared TiO2 electrode are first analyzed by using several diagnostic techniques. In particular, by extensive cathodoluminescence and photocurrent measurements it is possible to determine the energy band diagram of the material intragap levels and to observe their influence in both radiative and photoinduced transport properties. The TiO2 electrodes have been annealed at 500 degrees C for 1, 4, and 8 h in argon or in oxygen environment and then used to develop different DSSCs. The oxygen annealed solar cells show a monotonic increase in the efficiency from 6.75 up to 7.30; meanwhile, the argon-annealed solar cells have an efficiency that remains slightly constant around 6.85. By comparing the behavior of all cells parameters with the CL properties of the annealed TiO2 electrodes, it is possible to determine a correspondence between the short circuit current densities of the DSSCs and the variation of the intragap states in the semiconductor layer induced by annealing.