Abstract

Several donor-acceptor π-conjugated copolymers were synthesized by combining 4,7-bis(3,3’/4,4’- hexylthiophene-2-yl)benzo[c][2,1,3]thiadiazoles (HT-BzT-HT) with different donor segments, including thiophene, 2,2`-bithiophene, thieno[3,2-b]thiophene and dithieno[3,2-b;2’,3’-d]thiophene via Stille cross-coupling methodology, under microwave irradiation. All copolymers exhibited good solubility in most common organic solvents and showed high thermal stabilities. The revealed relationships between the molecular structure and optoelectronic properties were discussed. Each of DFT/TDDFT theoretical calculations and experimental measurements showed that moving the hexyl side chains from 3,3’- to 4,4’- positions in the thiophene rings of HT-BzT-HT units leads to a decrease both optical and electroChemical band gaps. Electrochemical characterization showed that the estimated HOMO and LUMO energy levels are in the range of -5.18 eV to -5.60 eV and -3.25 to -3.53 eV, respectively. The PCE of 1.91% was obtained from P10/PC60BM based device with Voc of 0.64 V, Jsc of 5.68 mA/cm2 and fill factor of 64%.

Keywords: π-conjugated copolymers; Solar cell; Benzothiadiazole; Cross-coupling