Modulation of Optoelectronic Performance in N-alkyl-dithieno[3,2 b:2',3' d]pyrrole based Organic Dyes: Insights from DFT/TD-DFT.

The present study focuses computational design and theoretical evaluation of ten different donor-π-acceptor (D-π-A) organic dyes F (1-10), for dye-sensitized solar cell (DSSC) applications. The dye molecules are incorporated using 4-methyl-4H-dithieno[3,2-b:2',3'-d]pyrrole π-bridge combined with different electron-donating groups, including amino, dimethylamine, methoxy, and diphenylamine, along with electron-withdrawing acceptors such as nitro (-NO₂), cyano (-CN), cyanoacrylic acid (CAA), 4,5-dicyanoimidazole (DCI), and 5,6-dicyanobenzoimidazole (DCBI). Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have been performed to investigate the electronic, optical, and photovoltaic properties. The optimized dyes exhibit narrow energy gaps (2.67- 4.00 eV) and strong intramolecular charge-transfer (ICT) characteristics with absorption maxima ranging from 312.5 nm to 564.3 nm. Organic dyes with CAA, DCI and DCBI units significantly enhance ICT strength, red-shifts absorption spectra, and improve electron injection efficiency. The calculated open-circuit voltages ([Formula: see text]) span from 1.18 V to 1.41 V, while light-harvesting efficiencies (LHE) reach up to 96.57%. The photovoltaic analysis shows outstanding device performance, with short-circuit current densities ([Formula: see text]) reaching 32.3 mA cm⁻2 and power conversion efficiencies (PCE) up to 37.8%. Collectively, these results underscore the potential of the proposed dyes as high-efficiency sensitizers for next-generation DSSC applications.