Quantum simulation of benzothiadiazole-based D-π-A-π-D dyes for enhanced optoelectronic and photovoltaic performance in DSSCs

In this study, a theoretical investigation of four organically symmetric benzothiadiazole-based D-π-A-π-D dyes (D1–D4) was performed in order to evaluate their potential as photosensitizers in dye-sensitized solar cells (DSSCs). Their structural, electronic, optical, and charge transport properties were analyzed using DFT and TD-DFT methods at the B3LYP/6-31G(d,p) level. Frontier molecular orbital analysis reveals an effective spatial separation between donor and acceptor regions, facilitating intramolecular charge transfer upon photoexcitation. The calculated band gaps range from 2.26 to 2.60 eV, suggesting that the dyes can absorb light in the visible range, as the LUMO levels (-2.29 to -2.47 eV) are well positioned above the conduction band of TiO2, allowing for thermodynamically favorable electron injection. The simulated UV-visible spectra show strong absorption bands dominated by HOMO → LUMO excitations, indicating a pronounced intramolecular charge transfer character. The photovoltaic parameters, such as open-circuit voltage, Gibbs free energy of electron injection, and charge transfer rates, indicate efficient electron injection for all dyes, with a particularly promising performance by D1 and D3 due to their high electron affinities and favorable electron transfer, thus validating the potential of these dyes for next generation DSSC applications.