Density-controlled ZnO/TiO2nanocomposite photoanode for improving dye-sensitized solar cells performance

Abstract

Dye-sensitized solar cells (DSSCs) via ZnO/TiO 2 nanocomposite photoanode with density-controlled abilities are presented in this paper. This nanocomposite photoanode is composed of TiO2 nanoparticles dispersed into densitycontrolled vertically aligned ZnO-TiO 2 core-shell nanorod arrays. The density-controlled ZnO-TiO 2 core-shell nanorod arrays were synthesized directly onto fluorine-doped tin oxide (FTO) substrates using an innovative two-step wet chemical route. First, the density-controlled ZnO nanorod arrays were formed by applying a ZnO hydrothermal process from a TiO 2 nanocrystals template. Second, the ZnO-TiO 2 core-shell nanorod arrays were formed by depositing a TiO 2 shell layer from a sol-gel process. The major advantages of a density-controlled ZnO/TiO 2 nanocomposite photoanode include (1) providing a better diffusion path from ZnO nanorod arrays and (2) reducing the recombination loss by introducing an energy barrier layer TiO 2 conformal shell coating. To validate the advantages of a density-controlled ZnO/TiO 2 nanocomposite photoanode, DSSCs based on a ZnO/TiO 2 nanocomposite photoanode were fabricated, in which N719 dye was used. The average dimensions of the ZnO nanorod arrays were 20 μm and 650 nm for the length and the diameter, respectively, while the designated spacing between each nanorod was around 5 μm. The performance of the solar cell was tested by using a standard AM 1.5 solar simulator from Newport Corporation. The experimental results confirmed that an open-circuit voltage, 0.93 V, was achieved, which was much higher than the conventional TiO 2 nanoparticles thin film structure for the same thickness. Thus, density-controlled ZnO/TiO 2 nanocomposite photoanodes could improve the performance of DSSCs by offering a better electron diffusion path.