Directly grown anatase TiO₂ films via liquid phase deposition as the photoanodes for dye-sensitized solar cells

Graphical abstract: Gradient TiO₂ photoanodes prepared by liquid phase deposition, which gained an efficiency as high as 6.51%. - Highlights: • An alternative way to fabricate DSSC photoanode via liquid phase deposition was presented. • DSSC with TiO₂ films first deposited at a higher temperature (80 °C) and subsequently at a lower temperature (60 °C) with an efficiency of 6.51%. • EIS indicated the two-temperature deposited TiO2 film had a lower resistance as well as a longer electronic lifetime. - Abstract: Anatase TiO₂ films were directly grown on the conductive glass by liquid phase deposition (LPD) and used as the photoanodes of dye-sensitized solar cells (DSSCs). TiO₂ films deposited at a higher temperature had a wider pore size distribution and a perfectly interfacial binding with the conductive FTO layer, while the ones deposited at a lower temperature presented a higher specific surface area to adsorb more dye so that the DSSCs with such two-temperature deposited gradient TiO₂ films had the enhanced performance significantly. Moreover, deposition at 80 °C showed a higher deposition rate and TiO₂ in the derived films was in a large crystallite size as well as a larger particle size, but a longer duration resulted in some single-crystal particles through the dissolving-precipitation mechanism, which were not suitable to the photoanodes. Thus, gradient TiO₂ films were firstly deposited at 80 °C and subsequently at 60 °C for a varying duration to efficiently tune their thickness. The DSSCs with the gradient TiO₂ film photoanodes presented a short-circuit current density of 14.9 mA cm⁻² and an energy conversion efficiency of 6.51%. For a comparison, LPD TiO₂ film without gradient structure was prepared at a fixed temperature (60 °C), which presented a short-circuit current density and photo-to-electric conversion efficiency of 8.78 mA cm⁻² and 4.39%, respectively. The electrochemical impedance spectroscopy (EIS) analysis indicated the DSSCs with TiO₂ films via two-stage deposition had a lower charge transfer resistance at TiO₂/dye/electrolyte interface and a longer electronic lifetime.