Improved short-circuit current density of dye-sensitized solar cells aided by Sr,Nb co-doped TiO2 spherical particles derived from sol-gel route

This study comes up with a uniform electrode containing Sr,Nb co-doped TiO2 particles for dye-sensitized solar cell applications. The spherical particles with the average diameter around 2.5 A mu m are composed of small nanoparticles with the average grain size of 60 nm. X-ray diffraction reveals that the introduction of dopants not only inhibits the growth of rutile phase, but also results in smaller primary crystallites, improving the surface area and dye adsorption ability of the electrodes. X-ray photoelectron spectroscopy shows Sr2+ and Nb5+ ions to be well incorporated into the titania crystal lattice without forming specific strontium or zinc compositions. UV-Visible spectra show that the co-doped TiO2 films have lower band gap energy than the undoped-TiO2, extending the absorption of TiO2 into visible region. Isolated energy levels in the band structure of TiO2 as well as local lattice distortions due to dopants introduction are the parameters that enhance the short-circuit current density of the cells. The TiO2 DSC co-doped with 0.075 at% Sr and 3 at% Nb (i.e., S7N3 cell) has the highest power conversion efficiency of 7.97 % as a result of less recombination, which is demonstrated by electrochemical impedance spectroscopy.