The Critical Impact of π-Spacer Design on DSSC Efficiency: A Comparative Computational Analysis of Isolated and TiO₂-Adsorbed Dyes

In this work, ten new coumarin-derived organic dyes were designed by restricting bithiophene rotation via substituent addition. Their structural, electronic, photovoltaic, and spectroscopic properties were examined through density functional theory calculations. Additionally, the electronic absorption spectra and charge-transfer characteristics of the dyes in ethanol were computed using time-dependent density functional theory (TD-DFT), along with molecular properties such as geometric parameters, optoelectronic properties, and frontier molecular orbitals. The findings show that all dyes display visible absorption in the range 401.59-617.32 nm, with band gaps of 1.90-2.57 eV, good light-harvesting efficiency, and substantial intramolecular charge-transfer capabilities. Furthermore, the study focused on the electrochemical and energy characteristics of dyes connected to the semiconductor TiO 2 . The findings suggest that these substances could be employed as sensitizers in DSSC applications.