Improved performance of flexible dye-sensitized solar cells by introducing an interfacial layer on Ti substrates

The recombination reaction of injected electrons with triiodide ion in the electrolyte limits the efficiency of dye-sensitized solar cells (DSSCs). This study reports the preparation of a sponge-like and conformal TiO₂ underlayer by hydrogen peroxide oxidation of Ti foil. This underlayer serves as a charge recombination barrier layer at the nanocrystalline TiO ₂/substrate interface, and suppresses the recombination reaction. This sponge-like TiO₂ underlayer increases the electrical contact area between the Ti substrate and nanocrystalline TiO₂, helping nanocrystalline TiO₂ attach to the Ti substrate. This study compares the performance of DSSCs that were subjected to different Ti surface treatments. Electrochemical impedance spectroscopy results confirm that the proposed sponge-like TiO₂ underlayer increased the open-current voltage (V_OC) and fill factor (FF) due to prolonged electron life time (τ_eff), and minimized resistance at the TiO₂/Ti interface (R_CT). With an optimal thickness of nanocrystalline TiO₂ and concentration of I₂, we achieved a conversion efficiency of 6.75% for a back-illuminated DSSC.