Influence of TiCl4 treatment on back contact dye-sensitized solar cells sensitized with black dye

To better understand why titanium tetrachloride (TiCl4) treatment improves short circuit current, we studied its effects on back contact dye-sensitized solar cells sensitized with black dye [tri(thiocyanato)(4,4',4 ''-tricarboxy-2,2':6',2 ''-terpyridine) ruthenium(II), Ru(tcterpy)(NCS)(3)] using transient absorption spectroscopy and electrochemical impedance spectroscopy. We found that the TiCl4 treatment improved short circuit current and achieved an overall energy conversion efficiency of 8.9%. The transient absorption signals did not change as a result of the treatment, suggesting that electron injection efficiency is not affected by the treatment. The impedance related to electron transport between TiO2 particles decreased and the peak frequency of the imaginary part of the electrochemical impedance spectra assigned to electron transfer from TiO2 to the redox couple was shifted to lower frequency by the treatment. This clearly indicates that TiCl4 treatment improved electron transport in the nanocrystalline TiO2 film in back contact dye-sensitized solar cells.