Density functional theory (DFT) and time - dependent density functional theory (TDDFT) studies of selected ancient colourants as sensitizers in dye-sensitized solar cells

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