Structurally modulated D-π-D-A(Semiconductor) anchoring dyes to enhance the tunable NLO response: a DFT/TDDFT quest for new photovoltaic materials

Abstract

In this paper, we designed new dyes (D-1 to D-5) with anchoring groups to test their stability for semiconductor surfaces with silyl unit as dye-sensitized solar cells (DSSCs). To investigate their photovoltaic efficiency, density functional theory (DFT) calculations were conducted with these novel D-π-D-A(Semiconductor) type structures using N,N-dimethylaniline and benzenesulfonate as electron donor (D) and a thiophene as π-conjugated spacers, with different semiconductor units as anchoring and electron acceptor units. A new dye structure as a reference (Ref-D) had been extended from methyl orange (MO) molecular structure with electron acceptor semiconducting units to improve the electronic transmission and increased maximum absorbance (λmax) to derive these new dyes (D-1 to D-5). The computed λmax of MO was obtained by testing DFT functional to benchmark it with its experimental λmax. Out of these functionals, the Coulomb-attenuating Becke, 3-parameter, Lee–Yang–Parr (CAM-B3LYP) functional having hybrid and long range correlation with 6-31G + (d,p) produced a nearly similar λmax (459 nm) as of its experimental one (464 nm). Their ionization potentials (I1) ranged between 2.65 and 5.31 eV which showed their good electron-donating nature. Their λmax values ranged between 532 and 565 nm which had a considerable red shift from Ref-D (465 nm). The highest second-order nonlinear optical (NLO) response of 134,532 Debye-Angstrom−1 was noted for dye D-2 which had the shortest bandgap. The charge tripping analysis of all the dyes miscible with the Ref-D showed an exclusive shift from highest occupied molecular orbital (HOMO) of reference to lowest unoccupied molecular orbital (LUMO) of dye. The density of states (DOS) calculations were performed with the dye D-5 to show that electronic transmission was from the dye towards the semiconductor in an efficient way. The inclusion of thiophene as π-conjugated spacer resulted in a significant increase in absorbance peak at around 80 nm. The DFT computed results offered an insight upon design of novel DSSCs with silyl anchoring groups for improved stability and efficiency. The present research is in a kind of prediction to develop new NLO materials with D-π-A design involving semiconductor as anchoring groups to attach with a DSSC surface.