Enhanced N719 Dye Adsorption onto Ca and La Doped Mesoporous TiO2 Anodes for Dye-Sensitized Solar Cells

Abstract

Calcium (Ca) and lanthanum (La) doping into mesoporous TiO2 prevents nucleation and growth of particles during synthesis and calcination at high temperature, resulting in smaller particle sizes and a decrease in the band gap of TiO2. These collectively have a positive affect on the efficiency of dye-sensitized solar cells (DSSCs) when employed as the anode. When designing an effective DSSC anode, the efficiency of dye adsorption must also be considered. This work investigates the adsorption properties of N719 dye onto La and Ca doped mesoporous TiO2 anodes for DSSCs. Near edge X-ray absorption fine structure spectroscopy (NEXAFS) identified the presence of La and Ca dopants in the TiO2 nanoparticles. Performance of DSSCs with Ca and La doped mesoporous TiO2 anodes demonstrated that doping of TiO2 enhances the overall efficiency of the devices. Both doped TiO2 nanoparticles showed higher dye adsorption concentration than that of pure TiO2, as shown in Brunauer-Emmett-Teller (BET) characterization. By employing Langmuir and Freundlich isotherms, dye adsorption behaviour was modelled. Pure and Ca doped TiO2 demonstrated good correlation to both isotherms, whereas La doped TiO2 only showed good correlation with Langmuir isotherm. Irrespective of its single layer adsorption kinetics, 0.1 mol.% La doped TiO2 has shown the highest dye adsorption and efficiency due to increase in surface area and oxygen vacancies induced by La doping.