Preparation of brookite TiO2 nanoparticles with small sizes and the improved photovoltaic performance of brookite-based dye-sensitized solar cells

Brookite TiO2 nanoparticles with small sizes (hereafter denoted as BTP particles) were synthesized through the hydrothermal treatment of TiCl4 solution with Pb(NO3)(2) as an additive. The obtained BTP particles have a large specific surface area (similar to 122.2 m(2) g(-1)) and relatively uniform particle sizes (similar to 10 nm) with the coexistence of a small quantity of nanorods with a length of similar to 100 nm. When used as a photoanode material for dye-sensitized solar cells (DSSCs), the BTP particles show a much higher dye-loading content than the brookite TiO2 quasi nanocubes (denoted as BTN particles) with a mean size of similar to 50 nm and a specific surface area of similar to 34.2 m(2) g(-1) that were prepared through a similar hydrothermal process but without the addition of Pb(NO3)(2). The fabricated BTP film-based solar cell with an optimized film thickness gives a conversion efficiency up to 6.36% with a 74% improvement when compared to the BTN film-based one (3.65%) under AM 1.5G one sun irradiation, while the corresponding bilayer brookite-based solar cell by using brookite TiO2 submicrometer particles as an overlayer of the BTP film displays a significantly enhanced efficiency of 7.64%. Both of them exceed the current record (5.97%) for the conversion efficiency of pure brookite-based DSSCs reported in the literature. The present results not only demonstrate a really simple synthesis of brookite TiO2 nanoparticles with both high phase purity and a large surface area, but also offer an efficient approach to improve the photovoltaic performance of brookite-based solar cells by offsetting brookite's inherent shortages such as lower dye-loading and poor conductivity as compared to anatase.