In situ preparation of hierarchically structured dual-layer TiO2 films by E-spray method for efficient dye-sensitized solar cells

Abstract Hierarchically-structured mesoporous TiO 2 films are prepared by the electrospray (E-spray) method. The microstructures of TiO 2 films can be feasibly tuned as spheres or nanocrystalline-mixed spheres, rendering in situ preparation of TiO 2 dual-layer. With these dual-layer TiO 2 films as photoanode and N719 as sensitizer, the dye-sensitized solar cell achieves a power conversion efficiency (PCE) of 8.96%, which is among the best of N719 devices so far, and constituting up to 19% improvement relative to single-layer TiO 2 photoanode based devices. To disclose the mechanism for the improvement, corresponding samples are prepared and investigated by scanning electron microscopy, electrochemical impedance spectroscopy, diffuse reflectance spectra. It was found that the dual-layer photoanode can simultaneously incorporate high dye loading and low charge transfer resistance, leading to high short current density and thus high PCE. Different to other reported dual-layer photoanodes, which often need two or more preparing procedures, only one step is needed in this work. To our best knowledge, it is the first time to employ only one step to in situ prepare photoanodes with dual-layer structures, which greatly simplifies the experimental processes.