Ultrathin Conformal Coating and Zn Doping in Nanocrystalline Mesoporous TiO2 Micron-Sized Beads for Highly Efficient Dye Sensitized Solar Cells

Doping in TiO2 has significant influence on donor density and dielectric parameters of TiO2 along with the introduction of defect levels. These variations in TiO2 hence could be exploited for enhancement in light scattering, charge transport and charge injection efficiency at the same time if the photoanode structure is properly designed. Herein, we attempted to demonstrate that Zn doping in nanocrystalline mesoporous TiO2 microspheres can be harnessed for such synergistic enhancements to realize a desirable photoanode for dye sensitized solar cells. A trace amount of Zn doping (2 at.%) along with resulting oxygen vacancies caused 69% enhancement in charge transport in electrode film, while the formation of an ultrathin disordered oxide layer (∼2 nm) on the surface of the nanocrystals drastically improved the charge injection efficiency by restraining recombination at the interface between the electrode and electrolyte. Furthermore, compositional variation upon Zn doping altered the dielectric parameters which resulted in ∼28% enhancement in light scattering efficiency over a broad spectrum of sunlight. An overall 26% improvement in energy conversion efficiency has been achieved by exploiting these structures in dye sensitized solar cell devices.