The effect of Lanthanum ions (La3+) on charge trapping in dye-sensitized solar cell (DSSC) photoanodes has been investigated with doped and surface-treated TiO2 nanoparticles. Doped nanoparticles consisting of 0.5 mol.% Mg and La co-doped TiO2, 0.5 mol.% Mg doped TiO2 and pure TiO2 were synthesized by the sol gel method. Surface-treated nanoparticles of Mg doped TiO2 and pure TiO2 were prepared by ball milling in 0.05 M aqueous La3+ solution. All materials were analyzed by XRD, XPS and UV–Vis DRS. Cell performance, surface free energy state changes and electron injection efficiency of DSSCs based on these nanoparticles were evaluated using current –voltage measurements, EIS and Incident photon to current conversion efficiency. Doped materials had La and Mg ions incorporated into the TiO2 lattice, while no lattice changes were observed for the surface-treated materials. Less visible light was absorbed by treated oxides compared with doped oxide samples. The overall power conversion efficiencies (PCE) of DSSC photoanodes based on doped materials were twice those of photoanodes fabricated from treated nanoparticles. Doping establishes deep traps that reduce the recombination of electron–hole (e–h) pairs. Conversely, the presence of absorbed oxygen in treated materials enhances e–h recombination with electrolyte at surface trap sites.
Materials Chemistry and Physics / Vol. 172, pp.105-112