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.