Role of Modifying Photoanodes by Organic Titanium on Charge Collection Efficiency Enhancement in Dye-Sensitized Solar Cells

Mesoporous TiO2 photoanodes are prepared by an electrophoretic deposition (EPD) method and applied in dye-sensitized solar cells (DSSCs). Pretreating an F-doped SnO2 coated glass (FTO) substrate and post-treating a TiO2 film to introduce an anatase TiO2 layer on the FTO and the TiO2 film, respectively, can greatly improve the power conversion efficiency (PCE) of a DSSC, which constitutes up 31% improvement compared with the untreated device. To disclose the mechanism for improvement, scanning electron microscopy, electrochemical impedance spectroscopy, open-circuit voltage decay, and photoluminescence spectra are investigated. It is proposed that the preformed compact TiO2 layer can suppress the back recombination by preventing direct contact between the electrolyte and the FTO substrate. Moreover, the compact TiO2 layer can reduce contact resistance between FTO and TiO2 particles. Further increased PCE by post-treatment is attributed to the promoted charge transfer efficiency. Both pre- and post-treating strategies can offer a reference to enhance the PCE for other porous film-based DSSCs, as well as promote the application of EPD in DSSCs.