Yolk@shell anatase TiO ₂ hierarchical microspheres with exposed {001} facets for high-performance dye sensitized solar cells

We report a facile, template-free and nontoxic one-pot solvothermal route for synthesizing submicrometer-sized yolk@shell hierarchical spheres, which possess a permeable shell self-assembled by ultrathin anatase TiO ₂ nanosheets (NSs) with nearly 90% of exposed {001} facets and mesoporous inner sphere with a high specific surface area. Compared to the {001} faceted TiO ₂ NSs and standard Degussa P25, the anatase TiO ₂ yolk@shell hierarchical spheres (TiO ₂ YSHSs) were obtained with surface area up to 245.1 m ² g ^-1 and their submicrometer scale simultaneously promoted light scattering in the visible region. A light to electricity conversion efficiency (η) of 6.01% was achieved for the DSSCs with TiO ₂ YSHSs as its photoanode, under 100 mW cm ^-2 illumination, indicating 49.9% and 34.8% increases compared to the DSSCs with TiO ₂ NSs (4.01%) and the standard Degussa P25 (4.46%) as photoanodes, respectively. The enhancement can be mainly attributed to the higher dye loading on TiO ₂ YSHSs (4.35 × 10 ^-5 mol cm ^-2) than that of TiO ₂ NSs (3.14 × 10 ^-5 mol cm ^-2) and P25 (3.32 × 10 ^-5 mol cm ^-2); longer lifetime of the injected electrons in TiO ₂ YSHSs film (65.79 ms) than that of in TiO ₂ NSs film (57.90 ms); and the good capability of light scattering of TiO ₂ YSHSs in visible light region, which are confirmed by UV-vis spectrophotometer and electrochemical impedance spectroscopy (EIS). The growth mechanism of the TiO ₂ YSHSs has also been investigated in detail.