Dicyanoimidazole-based novel organic D-π-A dyes with improved photophysical and charge transport properties for efficient DSSCs: DFT/TD-DFT exploration

This study reports four novel organic D–π–A dye molecules (D1–D4) by employing 4,5-dicyanoimidazole (DCI) as the efficient acceptor unit. The dye molecules D1-D4 consist of amino group, dimethyl amine, -OCH 3 and diphenylamine as different electron-donors and thiazolo[5,4-d]thiazole as π-spacers. DFT and TD-DFT are employed to investigate the electronic structure, optical properties, NLO properties, electron injection driving force, and light harvesting efficiency ( LHE ) of these D-π-A organic dye molecules. The organic dye molecules exhibit relatively small energy gaps (E g ) in the range of 2.95–3.64 eV and λ max values between 345 and 494.1 nm, overlapping with AM1.5 G solar spectrum. The computed results demonstrate that introducing the acceptor unit with DCI enhances hole injection efficiency and intensifies the intramolecular charge-transfer (ICT), leading to a red-shifted absorption accompanied by a higher molar extinction coefficient. Additionally, the computed open-circuit voltages ( V oc ) are in the range of 1.35–1.64 eV, while the LHE values increase up to 95.38% – 97.36%, assuming better performance and could pave the way for the design and synthesis of such D-π-A organic dyes for future application in DSSCs.