Oriented hierarchical single crystalline anatase TiO2nanowire arrays on Ti-foil substrate for efficient flexible dye-sensitized solar cells

Abstract

Hierarchical anatase TiO₂ nanowire (HNW) arrays consisting of long single crystalline nanowire trunks and short single crystalline nanorod branches have been synthesized on Ti-foil substrate via a two-step hydrothermal growth process. The formation of the HNW arrays based on anatase TiO₂ nanowire (NW) arrays can be ascribed to the crystallographic relationship between trunk and branch. The power conversion efficiency of dye-sensitized solar cells (DSSCs) based on such a HNW photoelectrode (4.51%) shows a significant enhancement compared to TiO₂ nanowire (NW) array photoelectrode (3.12%) with similar thickness (∼15 μm in nanowire length), which can be attributed to more dye loading, superior light scattering ability and comparable electron transport rate for the former. Furthermore, flexible DSSC using TiO₂ HNW arrays on Ti substrate as working electrode and transparent PEDOT/ITO-PET prepared via in situelectrodeposition as counter electrode shows a comparable photovoltaic performance to the rigid Pt/FTO-glass cell. A power conversion efficiency as high as 4.32% (J_sc = 7.91 mA cm⁻², V_oc = 796 mV, FF = 0.69) is obtained for the first time for fully flexible DSSC based on hierarchical TiO₂ nanowire arrays and Pt-free counter electrode.