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Ancient dyes such as brazilin, brazilein, haematoxylin and haematein have wide applications such as dyestuff, microscopy stains, and also as traditional and modern medicines. However these dyes have not yet been explored as sensitizers in dye sensitized solar cells. In the present work theoretical studies of these dyes have been performed using concepts such as density functional theory and time-dependent density functional theory, with Gaussian’09W software at B3LYP/6-31g(d) level. All the calculations are with the inclusion of geometric optimization and solvation effect of ethanol. Various energy levels of the dyes, electron cloud density, dominant energy transition states, optical properties and deprotonation order (proton affinity) of the dyes were obtained. This information was helpful to evaluate the feasibility of the dyes in dye sensitized solar cell (DSSC) applications. The dominant energy transition state of all dyes was found to be HOMO → LUMO at the first excitation state. For all four dyes electron clouds at the lowest unoccupied molecular orbital (LUMO) level were found to be localized near or at the most probable hydroxyl group that may anchor to the semiconductor. Among the four dyes, brazilein and haematein displayed excellent optical properties (λ max, oscillator strength, absorption band at visible spectrum) exhibiting their potential in DSSC application. DOI: http://dx.doi.org/10.4038/jnsfsr.v42i2.6996 J.Natn.Sci.Foundation Sri Lanka 2014 42 (2): 169-175

This work report, for the first time, the co-doping of mesoporous TiO2 with Cd2+ and La3+ cations for improved performance of dye-sensitized solar cells (DSSCs). Cd2+ ions modify the TiO2 lattice interstitially and lower the band gap enabling better electron injection. La3+ ions, having a larger ionic radius compared to that of Ti4+ ions, occupy interstitial sites and modulate particle size which increase surface area, hence the dye adsorption. The result demonstrates that DSSC employed with 0.1 mol% Cd-La co-doped TiO2 anode an increase in power conversion efficiency of 24% compared to DSSC with pure TiO2 anode. The doping concentration has to remain low as not to completely transform the morphology of TiO2 and to decrease the number of oxygen vacancies forming trap sites for recombination. The selection of ionic radius of dopants is significant as they can modify the TiO2 lattice either by substitution or interstitial of titanium ions.