Rare-earth and Nb doping of TiO2 nanocrystalline mesoscopic layers for high-efficiency dye-sensitized solar cells

The improvement of dye-sensitized solar cells (DSSCs) performance can be realized by using rare-earth and Nb-doped TiO2 mesoporous photoelectrodes. The undoped, Nb-doped, and rare-earth-doped TiO2 mesoscopic layers were prepared using a sol–gel method followed by a hydrothermal treatment. The Nb content was varied from 0.7 to 2.7 mol.%. The samples of complex rare-earth titanium oxides with fluorite-like structure containing Nb were synthesized using mechanical activation method. A series of fluorite-like Sm2[TixNb1–x]2O7 compounds with varied Nb content was synthesized. The structure and morphology of obtained materials were characterized using XRD, SEM, and optical absorption spectroscopy. The prepared TiO2 mesoscopic layers were used for fabrication DSSCs. We have found that the photovoltaic parameters of DSSCs based on TiO2 sensitized with N719 dye, are closely related to the electronic structure of the Nb-doped TiO2 electrodes. The changes of short circuit current of DSSCs were explained in relation to the electronic structure of the TiO2 electrodes. We have shown that the Nb doping enhances the junctions between neighboring nanoparticles and decreases the bulk electrical resistivity of the TiO2 electrodes. For the TiO2 electrodes doped with Nb the best DSSC performance with the energy conversion efficiency of 9.7% was obtained for Ti0.983Nb0.017O2 compound with 1.7 mol.% of Nb. Thus we have improved the device efficiency by 9% in comparison with the DSSC based on undoped TiO2 electrode. The developed rare-earth doped compounds SmTiNbO were also used for fabrication and characterization of DSSCs. However, unlike Nb-doped TiO2 layers, the efficiencies of DSSCs based on Nb-doped complex rare-earth titanium oxides were low in comparison with undoped TiO2.