Computational analysis of chalcogen-enhanced triphenylamine–based D-π-A sensitizers for DSSCs: a DFT study

Computational analysis of nine designs of triphenylamine-based sensitizers with donator-π-bridge-acceptor (D-π-A) structure for dye-sensitized solar cells (DSSC) was carried out via density functional theory (DFT). The purpose of this work was the modification of dye CP-II to improve the properties in DSSC with a series of changes using halogens like fluorine and chlorine in the donor group and chalcogens in the π-bridge. M06/6-31G(d) and M06/6-31G(d) + DZVP levels of calculation were utilized to determine ground state geometry optimization, frontier molecular orbitals, and their energy levels. The LUMO levels ranged from − 2.402 to − 2.568 eV, making them suitable for electron injection into the TiO₂ conduction band. Chemical reactivity parameters such as chemical hardness (η), electrophilicity index (ω), electroaccepting power (ω⁺), and electrodonating power (ω⁻) were studied. After their analysis, these values proved suitable for use as sensitizers. The free energy of electron injection (∆G_inject) was calculated with values between 1.203 and 1.683 eV, indicating a sufficient driving force for electron injection. Light-harvesting efficiency (LHE) and excited-state lifetime (τ) were estimated and analyzed. Time-dependent density functional theory (TD-DFT) with M06-2X/6-31G(d) and M06-2X/6-31G(d) + DZVP levels of calculation were used to determine the absorption wavelengths, oscillator strengths, and electron transitions. The incorporation of tellurium and selenium in the π-bridge reduced the HOMO–LUMO gap, enhanced charge transfer, and increased chemical stability. The best-performing sensitizer, MeTTe, exhibited a HOMO–LUMO gap of 2.715 eV, a high electrophilicity index (3.51 eV), and a long excited-state lifetime (9.73 ns).