Characterization of the photoelectron behavior of working electrodes modified with a titanium-dioxide window layer in dye-sensitized solar cells

Titanium dioxide (TiO₂) is currently used as a working electrode in dye-sensitized solar cells (DSSCs). The conventional working electrode is comprised of an absorption layer (with a TiO₂ particle size of ~20 nm) and a scattering layer (with a TiO₂ particle size of ~300 nm) on a fluorinedoped tin-oxide (FTO) substrate. In this study, we inserted a window layer with a 10-nm TiO₂ particle size between the FTO substrate and the absorption layer in order to increase both the transmittance and the specific surface area of the TiO₂. Electrochemical impedance spectroscopic analysis was conducted to characterize the electronic behavior of the working electrode. The Bode phase plot and the Nyquist plot were interpreted to determine the impact of the insertion of the window layer on the internal resistance of the DSSC and on the carrier lifetime. The photocurrent from the cell increased due to an increase in the specific surface area, which was a result of the addition of the window layer with a smaller particle size (10 nm). Further, the insertion of the window layer in the working electrode was found to lead to an effective increase in the transmission of the incident light. Therefore, The insertion of the window layer it was concluded to contribute to an increased conversion efficiency in the DSSCs.