Synthesis and characterization of a novel BT-Cz-3HT2 donor-acceptor conjugated via oxidative polymerization: Potential for optoelectronic applications

This study presents the synthesis via oxidative polymerization and in-depth characterization of a novel donor-acceptor conjugated terpolymer, BT-Cz-3HT2, incorporating benzothiadiazole (BT), carbazole (Cz), and 3-hexylthiophene (3HT) units. This approach offers a cost-effective alternative to traditional coupling methods like Suzuki or Stille, enabling scalable production while maintaining regioregularity. The material exhibits high thermal stability (Tg = 109 °C, onset decomposition >232 °C) and broad optical absorption up to 550 nm, featuring a strong intramolecular charge transfer (ICT) band at 430 nm indicative of efficient donor-acceptor interactions. The optical bandgap of 2.15 eV, confirmed by UV–vis and DFT/TDDFT studies, is narrower than those of the individual homopolymers (BT ∼3.0 eV, Cz ∼3.5 eV), suggesting enhanced conjugation. Structural integrity was verified using NMR and FTIR, while theoretical predictions closely matched experimental photophysical data, validating the proposed structure-property correlations. Compared to similar Cz-BT copolymers (PCE ∼4–6 % in OSCs), the incorporation of 3HT units improves solubility and hole mobility potential. These attributes position BT-Cz-3HT₂ as a promising candidate for optoelectronic applications, particularly low-cost organic solar cells and field-effect transistors.