Layer-by-layer self-assembly of TiO2 hierarchical nanosheets with exposed {001} facets as an effective bifunctional layer for dye-sensitized solar cells.

Layer-by-layer self-assembled TiO2 hierarchical nanosheets with exposed {001} facets have been successfully fabricated via a simple one-step solvothermal reaction. The anatase TiO2 layer-by-layer hierarchical nanosheets (TiO2 LHNs) exhibit favorable light scattering effect and large surface area, owing to their layer-by-layer hierarchical structure. When applied to the dye-sensitized solar cells (DSSCs), the layer-by-layer hierarchical structure with exposed {001} facet could effectively enhance light harvesting and dye adsorption, followed by increasing the photocurrent of DSSCs. As a result, the photoelectric conversion efficiency (η) of 7.70% has been achieved for the DSSCs using TiO2 LHNs as the bifunctional layer, indicating 21% improvement compared to the pure Degussa P25 (6.37%) as photoanode. Such enhancement can be mainly ascribed to the better light scattering capability of TiO2 LHNs, higher dye adsorption on TiO2 LHN {001} facets, and longer lifetime of the injected electrons in TiO2 LHNs compared to P25, which are examined by UV-vis spectrophotometry and electrochemical impedance spectroscopy under the same conditions. These remarkable properties of TiO2 LHNs make it a promising candidate as a bifunctional scattering material for DSSCs.