Construction of a branched ZnO–TiO2 nanorod array heterostructure for enhancing the photovoltaic properties in quantum dot-sensitized solar cells

Abstract

We reported a facile fabrication of three dimensional (3D) branched ZnO–TiO₂ heterojunction nanorod arrays using a two-step hydrothermal method. This process included the vertical growth of TiO₂ nanorod arrays on FTO substrates as backbones and then the facile solution growth of branched ZnO nanorods on the rutile trunks. After being decorated by CdS quantum dots (QDs), the branched ZnO–TiO₂ heterojunction nanorod arrays were used as photoanodes in quantum dot-sensitized solar cells (QDSCs). Compared to the bare TiO₂ nanorod arrays, the branched ZnO–TiO₂ heterojunction nanorod arrays provided a higher surface area for QD loading and better light scattering arising from ZnO nanorod branches. In the meantime, the heterojunction formed at the TiO₂–ZnO interface facilitated the electron transfer and reduced the recombination reactions of electrons with electrolyte-oxidized species. As a result, we got a conversion efficiency of 0.73% with the thickness of only 1 μm, which showed a 55% improvement over the QDSCs that used bare TiO₂ nanorod arrays as photoanode.