Non-Linear Optical Properties of Carbazole based Dyes Modified with Diverse Spacer Units for Dye-Sensitized Solar Cells: A First Principle Study

Density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations were performed for evaluating the photophysical and photochemical properties of a sequence of carbazole based metal-free organic dyes modified using different pi-conjugation spacer units, such as thiopine, pyrrole, furan, thiazole and isoxazole. Moreover, the modified dyes were subjected to investigation towards their non-linear optical (NLO) features. The results revealed that dipole moment (mu), static polarizability (alpha), anisotropic polarizability (Delta a) and hyperpolarizability (first order (beta) and second order (gamma)) of modified dyes are considerably enhanced as a consequence of changing the spacer unit. Likewise, light harvesting efficiency and oscillator strength of the modified dyes are enhanced upon wavelength of absorption is red-shifted by influence of spacer moieties. We believe that our calculations provide a more profound physical perception on structural property relationship for carbazole based dyes and give a hint to create potential sensitizers for opto-electronic and dye-sensitized solar cell applications.