Exploring charge transfer effects on linear, non-linear optical, and dye-sensitized solar cell properties: A DFT and TD-DFT investigation of carbazole and aniline-based dyes

The efficacy of aniline and carbazole-based sensitizers used in dye-sensitized solar cells (DSSCs) is correlated with the trends in density functional theory (DFT) based charge transfer (CT) and non-linear optical (NLO) properties since both DSSC and NLO properties highly rely on CT properties. The aniline-based donors showed a higher degree of planarity over carbazole-based donor sensitizers. This improved planarity in aniline-based sensitizers is attributed to efficient charge transfer and higher dipole moment. The efficient CT within the sensitizers is confirmed with bond-length alternation (BLA), bond order alternation (BOA), and quinoid character (QC). A direct correlation of band-gap (EG) with μ, ω, η, and Γ is witnessed. Time-dependent DFT (TD-DFT) results of vertical excitation demonstrated similar trends that are observed practically. Indeed, we observed a direct correlation between α and β and the experimentally observed DSSC efficiency. DFT and TD-DFT methods, linear, employed for computing the CT and linear and DSSC properties as implemented in Gaussian 09. NLO properties were simulated through single-point polar calculations. B3LYP and PBE1PBE functionals were used for geometry optimization. The linear and NLO properties were determined in various functionals, that is, global hybrid and range-separated hybrid functionals. A polarizable continuum model (PCM) was used for solvation studies. To understand the realistic picture of the dye@TiO2 cluster, dye bound on TiO₂ clusters were optimized using a LANL2DZ basis set specifically for the Ti atom.