Double-layer composite film based on sponge-like TiO2 and P25 as photoelectrode for enhanced efficiency in dye-sensitized solar cells

A TiO2 double-layer composite film consisting of hierarchically sponge-like macro-/mesoporous TiO2 (HSMM-TiO2) as overlayer and commercial-grade TiO2 nanoparticles (P25) as underlayer is designed as the photoelectrode of dye-sensitized solar cells (DSSCs). The photoelectric conversion performances of DSSCs based on P25 nanoparticle film, HSMM-TiO2 film, and P25/HSMM-TiO2 double-layer composite film are investigated and compared. It is found that the overall energy-conversion efficiency of 5.48% is achieved by the formation of P25/HSMM-TiO2 double-layer composite film, which is 51.4% higher than that formed by P25 nanoparticle film (eta = 3.62%) and 27.1% higher than that formed by HSMM-TiO2 film (eta = 4.31%) under identical film thickness (ca. 20 mu m) at a constant irradiation of 100 mWcm(-2). The enhanced conversion efficiency of TiO2 double-layer composite film can be attributed to the combined effect of the following factors. The HSMM-TiO2 overlayer enhances light-harvesting efficiency due to its intense light scattering and the P25 nanoparticle underlayer ensures good electronic contact between TiO2 film and the F-doped tin oxide (FTO) glass. Furthermore, the high specific surface area and special pore-wall structure of HSMM-TiO2 are respectively beneficial to adsorption of dye molecules and transport of both electrons and electrolytes. (C) 2012 Elsevier B. V. All rights reserved.