Application of hierarchical TiO2 spheres as scattering layer for enhanced photovoltaic performance in dye sensitized solar cell

Hierarchical TiO2 spheres (HTSs) composed of thin nanosheets with a high ratio of exposed (001) facets were prepared by solvothermal reaction of titanium precursor under the mediation of HF and glacial acetic acid (HAc). The size of the spheres and the density of primary nanosheets could be effectively tuned by simply adjusting HAc dosage. The as-prepared HTSs were highly crystallized and demonstrated high BET surface area, but decreased apparently after calcination due to the collapse or fusion of the primary nanosheets. The calcinated HTSs were further applied as scattering layers in photoanodes of dye sensitized solar cells (DSSCs). Compared with the monolayered nanospindle (NS) photoanode with similar thickness, the bilayered photoanodes with the HTSs as scattering layers offered dramatically higher photocurrent density (J(sc)) and therefore higher energy conversion efficiency (eta). Due to the highest scattering effect and the lowest charge transfer resistance (R-ct) at TiO2-dye-electrolyte interface, the DSSC with H2 (synthesized with HAc volume of 2 mL) as scattering layer offered eta of 7.72%, which is 42% higher than that based on the monolayered NS photoanode.