Abstract
New organic dyes (H1-H6) for their promising applications as dye sensitized solar cell (DSSCs) were theoretically designed from 6,6 '-di(thiophen-2-yl)-4,4 '-bipyrimidine (TB) moiety in acceptor (A), pi-spacer, and donor (D) type architecture to create A-pi-D-pi-D-pi-A framework. After their benchmarking study against various exchange correlation (XC) and long-range corrected (LC) functional, the CAM-B3LYP produced accurate results so as selected for further density functional theory (DFT) and time dependent DFT (TD-DFT) studies. The frontier molecular orbitals (FMOs) were analyzed for their electron transfer properties, and their energies of the highest occupied molecular orbital (E-HOMO) and the lowest unoccupied molecular orbital (E-LUMO) were used to assess various electronic properties. Their energy differences (EH-L) ranged between 1.69 and 2.03 eV indicating their good responsiveness to electron injection (G(inj)) being the values greater than 0.2 eV. The maximum absorbance of the dyes was reported around the 388-406 nm while their starting material (TB) had this value to be 371 nm. This redshift was significant with an intensification of electron-withdrawing groups on the dye structures. The dyes were evaluated for their device related parameters like their light harvesting efficiency, open circuit voltage, exciton binding energies, and exciton life times which were found in their promising values. The dyes were analyzed for their linear (alpha), first (beta(total)), and second (gamma(total)) order nonlinear responses and were found to have significantly higher responses, not only against their starting materials but also those reported in literature for standard molecules (urea and p-nitric acid). Among the dyes under study, dye H4 exhibits the highest molecular polarizability (alpha) and hyperpolarizability (beta and gamma) values thanks to two CN substituted units on each ends. These dyes are most likely to have possible optical and photonic uses. Also, according to the results of the current theoretical research, all of these dyes may function as effective photosensitizer for their DSSC application.