One-step synthesis of vertically aligned anatase thornbush-like TiO ₂ nanowire arrays on transparent conducting oxides for solid-state dye-sensitized solar cells

Herein, we report a facile synthesis of high-density anatase-phase vertically aligned thornbush-like TiO₂ nanowires (TBWs) on transparent conducting oxide glasses. Morphologically controllable TBW arrays of 9 μm in length are generated through a one-step hydrothermal reaction at 200 °C over 11 h using potassium titanium oxide oxalate dehydrate, diethylene glycol (DEG), and water. The TBWs consist of a large number of nanoplates or nanorods, as confirmed by SEM and TEM imaging. The morphologies of TBWs are controllable by adjusting DEG/water ratios. TBW diameters gradually decrease from 600 (TBW600) to 400 (TBW400) to 200 nm (TBW200) and morphologies change from nanoplates to nanorods with an increase in DEG content. TBWs are utilized as photoanodes for quasi-solid-state dye-sensitized solar cells (qssDSSCs) and solid-state DSSCs (ssDSSCs). The energy-conversion efficiency of qssDSSCs is in the order: TBW200 (5.2 %)>TBW400 (4.5 %)>TBW600 (3.4 %). These results can be attributed to the different surface areas, light-scattering effects, and charge transport rates, as confirmed by dye-loading measurements, reflectance spectroscopy, and incident photon-to-electron conversion efficiency and intensity-modulated photovoltage spectroscopy/intensity-modulated photocurrent spectroscopy analyses. TBW200 is further treated with a graft-copolymer-directed organized mesoporous TiO₂ to increase the surface area and interconnectivity of TBWs. As a result, the energy-conversion efficiency of the ssDSSC increases to 6.7 % at 100 mW cm^-2, which is among the highest values for N719-dye-based ssDSSCs. There′s something good behind the thorn: High-density anatase-phase vertically aligned thornbush-like TiO ₂ nanowires on transparent conducting oxide (TCO) glasses result in high-efficiency solid-state dye-sensitized solar cells, which exhibits one of the highest values observed for N719 dyes. This can be attributed to improved surface areas, light-scattering effects, and charge transport rates.