Designing high-efficiency sensitizers remains a central challenge for dye-sensitized solar cells (DSSCs). In this work, nineteen donor motifs commonly employed in the literature were screened to identify optimal donors and to assess the impact of donor substitution on the reference dye D0 (2-cyano-3-[2′-(2″-(4″-(dimethylamino)phenyl)ethynyl)thieno[3,2-b]thiophen-5′-yl]acrylic acid) with the goal of improving device performance. Using DFT/TD-DFT with the CAM-B3LYP functional, we characterized nineteen literature-derived donor motifs via their electronic absorption spectra and key photovoltaic descriptors. Donor substitution, most notably with D1, D3, D5, D6, and D15, substantially improves the electronic and optical properties, yielding lower HOMO energies, a reduced band gap (Egap), enhanced absorption intensity, and a bathochromic shift of the main band. Performance indicators, notably the electron-injection free energy (ΔGinj) and open-circuit voltage (Voc), indicate spontaneous, thermodynamically favorable electron injection from the excited dye into the TiO₂ conduction band.

Population growth and economic development have led to an increase in global energy consumption. Solar energy, a major renewable source, is essential to meeting human energy needs. This study, four new organic dyes (A1–A4) with a D–π–D–A structure using DFT and TD-DFT techniques for their potential application in dye-sensitized solar cells (DSSCs). The impact of π-bridge modifications of the A0 (reference molecule) on the structural, photovoltaic, optical and electronic properties was analyzed. The dyes showed band gaps (Egap) ranging from 2.4 to 3.5eV and absorption wavelengths (λ) from 420.16 to 627.4nm. Results suggest that the modification of the π-bridge of dye A0 enhanced intramolecular charge transfer (ICT). and improved hole injection. Theoretical open-circuit voltages (Voc) varied between 1.15 and 2.36 eV, while light harvesting efficiency (LHE) values ranged from 0.80 to 0.93. This study could effectively assist chemists in the synthesis of efficient dyes for DSSCs.

The FTIR and Raman spectra of dopamine were also recorded in the spectral region 20 - 4000 cm^-1 and 400 - 4000 cm^-1 respectively. The optimized molecular geometry and fundamental vibration frequencies are interpreted using structural optimizations based on the DFT method. The B3LYP / 6-311G (d, p) was used to determine the calculations of the chemical descriptor. The dopamine (DA) molecule can acquire a maximum charge of 0.513 eV from its environment. To understand the molecular interactions of Dopamine, the MEP is a crucial tool. Nonlinear optical descriptors (NLO) and the lengths, bond angles are also determined by DFT and MP2 methods. The DFT method was used to determine the chemical shifts of ¹H and ¹³C of the product. These constants have been calculated by employing the GIAO (Gauge-Including-Atomic-Orbit), CSGT (Continuous Set of Gauge Transformations) and IGAIM (Individual Gauges for Atoms In Molecules) methods at the B3LYP/6-311G (d, p). The comparison of the theoretical chemical shifts with the experimental ones shows that the CSGT method is the best.

The FT-IR spectrum of salicylic acid (SA) was studied in the region 10-4000 cm-1. The optimized molecular geometry and fundamental vibration frequencies are interpreted using structural optimizations based on the Functional Density Theory (DFT) method. Additionally, we used B3LYP / 6-311G (d, p) to determine the chemical descriptor, the ionization potential (I), the electron affinity (A), the chemical potential (μ), the chemical hardness (η). Nonlinear optical descriptors (NLO) such as dipole moment (μ), polarizability (α), first hyperpolarizability (β) and second hyperpolarizability (γ), 3D maps of HOMO and LUMO orbitals, lengths and Bond angles of salicylic acid isomers are also determined by both DFT and MP2 (The Møller-Plesset theory of order 2 perturbation) methods. The overall descriptors and the non-linear optical properties confirmed that salicylic acid is the reactive molecule and para-hydroxybenzoic acid is the stable molecule. An electrostatic molecular potential (MEP) study was also performed to determine the reactivity of molecules.