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.

In the current study, the DFT and TD-DFT methods are used to investigate seven donor–π-acceptor (D–π–A) dyes, named DY01 to DY07, which are planned for utilization in DSSCs. The HOMO-LUMO gaps are decreased due to the solvent effect by 0.05-0.16 eV and are smallest (1.85 eV) for DY01. Frontier molecular orbitals show that charge separation is efficient between triphenylamine donor and cyanoacrylic acid acceptor. The bathochromic shift due to the solvent effects is estimated by the TD-DFT calculations, and DY01 exhibits the maximum red shift (638 nm) as well as DY05 has the highest oscillator strength (f = 1.664). Photovoltaic parameters reveal that DY01 is the most efficient (0.958), and DY02 could receive the relatively better electrons injection strength accompanied with high Voc value. Adsorption on (TiO₂)₈ cluster has an additional decrease the energy gaps and DY01 and DY07 show strong red shifts. Upon adsorption, the orbital distribution shows strong electronic coupling conducive to photo-induced electron transfer to the semiconductor. It can be concluded that DY01 is the most efficient sensitizer showing highest quantum efficiency due to its narrow band gap, effective intramolecular charge transfer (ICT), high light-harvesting efficiency (LHE) and favorable interfacial properties.

Dye-sensitized solar cells (DSSCs) represent a highly promising new generation of photovoltaic devices that offer an attractive alternative to traditional silicon-based solar cells due to their low production costs, simple manufacturing, and adaptable optoelectronic properties. Titanium dioxide (TiO₂) is extensively utilized as a semiconductor in DSSCs due to the favorable position of its conduction band, high chemical stability, abundance, and non-toxicity. As part of this work, an in-depth computational study was conducted on five organic dyes (D1 to D5) to investigate their potential as effective sensitizers for DSSC applications. Density functional theory (DFT) and time-dependent DFT (TD-DFT) were employed to investigate their structural, electronic, and optical properties, as well as their key photovoltaic parameters. The HOMO energy levels calculated (−5.99 to −6.36 eV) were low enough to allow efficient dye regeneration by the electrolyte, while the LUMO levels (−3.05 to −3.71 eV) were located above the conduction band edge of TiO₂ (−4.0 eV), Calculated band gaps (2.35–2.94 eV) supported strong absorption in the visible range, and open-circuit voltages (0.26–0.94 eV) suggested good photovoltaic potential. Furthermore, all dyes presented positive free electron injection energy (ΔGinject), evidencing thermodynamically favorable charge transfer processes. Benchmarking revealed that structural modifications between dyes were found to be significantly.