Oriented hierarchical single crystalline anatase TiO_2 nanowire arrays on Ti-foil substrate for efficient flexible dye-sensitized solar cells

摘要

Hierarchical anatase TiO_2 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 TiO_2 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 TiO_2 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 TiO_2 HNW arrays on Ti substrate as working electrode and transparent PEDOT/ITO-PET prepared via in situ electrodeposition 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 TiO_2 nanowire arrays and Pt-free counter electrode.