Influence of the Sol-Gel pH Process and Compact Film on the Efficiency of -Based Dye-Sensitized Solar Cells

The influence of pH during hydrolysis of titanium(IV) isopropoxide on the morphological and electronic properties of TiO 2 nanoparticles prepared by the sol-gel method is investigated and correlated to the photoelectrochemical parameters of dye-sensitized solar cells (DSCs) based on TiO 2 films. Nanoparticles prepared under acid pH exhibit smaller particle size and higher surface area, which result in higher dye loadings and better short-circuit current densities than DSCs based on alkaline TiO 2 -processed films. On the other hand, the product of charge collection and separation quantum yields in films with TiO 2 obtained by alkaline hydrolysis is c.a. 27% higher than for the acid TiO 2 films. The combination of acid and alkaline TiO 2 nanoparticles as mesoporous layer in DSCs results in a synergic effect with overall efficiencies up to 6.3%, which is better than the results found for devices employing one of the nanoparticles separately. These distinct nanoparticles can be also combined by using the layer-by-layer technique (LbL) to prepare compact TiO 2 films applied before the mesoporous layer. DSCs employing photoanodes with 30 TiO 2 bilayers have shown efficiencies up to 12% higher than the nontreated photoanode ones. These results can be conveniently used to develop optimized synthetic procedures of TiO 2 nanoparticles for several dye-sensitized solar cell applications.