Enhancing optoelectronic properties of phosphonic acid based dyes via donor unit variation: A DFT/TD-DFT investigation

In this work, nine phosphonic acid-based dyes adopting the structure D-π-A′-π-A were designed and examined using the density functional theory (DFT) approach to assess their potential application in dye-sensitized solar cells (DSSCs). By incorporating various donor moieties, including carbazole, triphenylamine, phenothiazine, phenoxazine, and coumarin, the relevant key parameters to short-circuit photocurrent density and open-circuit voltage of the designed dyes were assessed. These parameters include the driving force of electron injection (ΔGinj), the spontaneity of dye regeneration (ΔGreg), the charge transfer distance (DCT), the reorganization energies, and the nonlinear optical (NLO) properties were computed. All calculations were performed via the implicit CPCM method in chloroform as solvent medium. The calculated results reveal that the incorporation of different donor units resulted in a narrower bandgap, higher molar extinction coefficient, red-shift in the absorption spectra, better intramolecular charge transfer, and increase in light-harvesting efficiency for dyes where the donor unit is connected by the phenyl in contrast to the T-shaped structure where the donor unit is connected via the nitrogen atom. These findings offer valuable insights into optimizing the optoelectronic properties of phosphonic acid-based dyes for potential use in DSSCs.