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.

Herein, we theoretically design four new π-conjugated thieno[3,4-b]pyrazine derivatives for organic solar cells (OSCs), denoted 2,3-di([2,2′:5′,2″:5″,2‴-quaterthiophen]-5-yl)-5,7-di(thiophen-2-yl)thieno[3,4-b]pyrazine, 2,3-bis(5'''-(4-fluorophenyl)-[2,2':5',2'':5'',2'''-quaterthiophen]-5-yl)-5,7-di(thiophen-2-yl)thieno[3,4-b]pyrazine, 2,3-bis(5'''-(4-methoxyphenyl)-[2,2':5',2'':5'',2'''-quaterthiophen]-5-yl)-5,7-di(thiophen-2-yl)thieno[3,4-b]pyrazine, and 2,3-bis(5'''-(9-methyl-9H-carbazol-2-yl)-[2,2':5',2'':5'',2'''-quaterthiophen]-5-yl)-5,7-di(thiophen-2-yl)thieno[3,4-b]pyrazine. The geometric, electronic, optical, photovoltaic, and nonlinear optical (NLO) properties of the investigated chemical structure were investigated using Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) calculations at the B3LYP/6-31G(d,p) level. Structural changes on the chemical structure induce a narrow energy gap in the range (2.08 – 2.12 eV), and an enhancement of the absorption in the visible range (λmax = 682 – 688 nm). In addition, a low value of exciton binding energies is obtained (Eb = 0.28 – 0.31 eV). Analysis of the density of states (DOS), transition density matrix (TDM), electron localization function (ELF), and localized orbital locator (LOL) showed effective charge delocalization and donor-to-acceptor electron transfer. The photovoltaic performance was assessed using the open circuit voltage (Voc) obtained between Highest Occupied Molecular Orbital (HOMO) donor to Lowest Unoccupied Molecular Orbital (LUMO) acceptor levels and was found promising (Voc = 1.32 – 1.44 V). The large hyperpolarizability and high nonlinearity response of the NLO results also indicated the potential for these molecules to be used in various optoelectronic applications.