Synthesis and characterization of dithienothiophene/benzothiadiazole based low band gap donor-acceptor copolymers for bulk hetero junction photovoltaic cells

► Two sets of novel co-polymers based on dithieno[3,2-b:2′,3′-d]]thiophene (DTT) derivative as a donor (D) and benzothiadiazole (BT) as an acceptor (A) were synthesized for BHJ solar cells. ► Structure activity relationship was discussed using D-π-A strategy in the polymer backbone. ► Incorporation of thiophene units as shorter conjugated spacers between donor and acceptor units facilitated tuning of the band gap and energy level with significant enhancement in the solar cell efficiency. ► DTT bridged with thiophene as a conjugated spacer appears to be a promising, quite simple, and useful co-monomer building block for photoactive polymer materials with solar cell applications.