Evaluation of defect levels formed in the nano-porous titanium oxide layer of dye-sensitized solar cell

The development of the dye-sensitized solar cell (DSC) has been expected to supply another solar cell other than the silicon solar cells, for its convenient production processes. The nano-porous titanium oxide (TiO₂) layer, photo-electrode of DSC, is constructed on a F-doped SnO₂ transparent electrode(FTO), before the dye deposition. The structure of the porous TiO₂ layer, such as the existence of charge traps, seems to influence the photoelectric conversion efficiency of DSC. The possibility of estimating the photo-electrode efficiency by the charge trap structure was studied with thermally stimulated current (TSC) measurement. As a result of the TSC measurement, four charge traps were detected in the electrode and were evaluated the energy trap depths of 0.07 eV, 0.138 eV, 0.385 eV and 0.381 eV. The escape frequency factors were also evaluated in large span from 10 s^-1 to 10⁸ s^-1.