Performance optimization in dye-sensitized solar cells with β-NaYF4:Er3+/Yb3+ and graphene multi-functional layer hybrid composite photoanodes

The β-NaYF4:Er3+/Yb3+ hexagonal submicro-prisms coated with SiO2 forming core-shell structures (NYFYE@SiO2) and graphene oxide have been synthesized via a hydrothermal route. These NYFYE@SiO2 prisms and graphene were both introduced into TiO2 nanocrystalline films to form multi-functional-layers hybrid composite photoanodes and their dye-sensitized solar cells (DSSCs). The influence of various hybrid architectures of the composite photoanodes on the performances of the photoanodes and DSSCs were explored. Studies revealed that the graphene doping obviously increased the dye absorbed in the photoanode, the short-circuit current density (Jsc) and photoelectric conversion efficiency (η) of the DSSC. The adding of the NYFYE@SiO2 prisms significantly increased the light scattering and near-infrared light harvesting of the photoelectrode, among which the SiO2 coating layer on the prisms played an important role in reducing the photoelectron recombination and thus increasing the Jsc of the DSSC. The Jsc and η of the DSSC were significantly enhanced due to the complementary role between the UC of the NYFYE@SiO2 and the graphene. The optimal properties with a Jsc of 14.63 mA/cm2 and η of 7.16% are obtained in the DSSC with the codoped composite photoanode, increasing significantly by 21.5% and 25.6%, respectively, in comparison with those of the DSSC with pure TiO2 photoanode. Our studies demonstrated that codoping in photoanode with materials of complementary functions is an effective way to improve the performance of DSSCs.