Solubilized 5,6-bis(octyloxy)benzoxadiazole as a versatile acceptor block for designing novel (-X-DADAD-)n and (-X-DADADAD-)n electron donor copolymers for bulk heterojunction organic solar cells

•The first benzoxadiazole-based (-X-DADAD-)n type copolymers were synthesized•Conjugated соpolymer with extended DADADAD units was designed•Deep-lying HOMO energy levels provided high VOC up to 0.9 V•The best performing polymer yielded PCE of 5.5% using PC70BM as acceptor

Three novel conjugated polymers incorporating extended DADAD and DADADAD building blocks with the 5,6-bisalkoxybenzoxadiazole acceptor (A) and the electron donor (D) thiophene units were synthesized and fully characterized. The application of the benzoxadiazole instead of benzothiadiazole resulted in a significant increase in the open circuit voltage of organic solar cells based on such polymers. The best performing material delivered a decent solar light power conversion efficiency of 5.5% in organic bulk heterojunction solar cells using PC71BM as an electron acceptor component. The obtained results revealed a high potential of using different acceptor building blocks in the design of novel (-X-DADAD-)n polymers with tailored optoelectronic and photovoltaic properties.