Flower-like TiO2 with highly exposed {001} facets used as scattering layers for dye-sensitized solar cells

Abstract

The TiO2 crystals of flower-like shapes (FF-TiO2) were prepared by a one-step hydrothermal reaction from the metallic titanium powders. The synthesized TiO2 particles exhibit truncated tetragonal bipyramidal morphologies, which has ∼30% of the surface enclosed by the {001} facets. The FF-TiO2 was employed as back-illumination photoanodes in fabricating the dye-sensitized solar cells (DSSCs). The power-conversion efficiency of the DSSCs was found to increase from 5.35% to 7.65% after incorporation of the FF-TiO2 into the P25 fabricated photoanodes. The specific structure and the dopant fluorine were proven to have great impacts on the lifetime (τn) for the photoelectrons to stay in the conduction band of TiO2 and the recombination time (τr) of the photogenerated electrons that would be quenched by the I3− ions. Reasons for the improvement in the photovoltaic properties have been clarified as follows: (1) the microsized particles were prepared within the optimum size region for Mie scattering; (2) the flower-shaped structured FF-TiO2 enhanced the saturated capacity for adsorption of dye molecules; and (3) the {001} facets with adsorbed fluorine (F−) at the surface could remove the trap states, and restrain the photoelectrons recombination between the photoanode and electrolyte.