New narrow bandgap polymers containing 10-(4-((2-ethylhexyl)oxy)phenyl)-10H-phenothiazine/phenoxazine and 3,6-di(2-thienyl)pyrrolo[3,4-c]pyrrole-1,4-dione)-based units: synthesis and photovoltaic properties

Diketopyrrolopyrrole (DPP) is one of the most used moieties in D–A conjugated polymers for high-performance π-extended conjugated polymer-based organic solar cells. The combination of 1,4-diketo-3,6-dithienylpyrrolo[3,4-c]pyrroles (DTDPPs) and the donor moieties 10-(4-((2-ethylhexyl)oxy)phenyl)-10H-phenothiazine (M1), 10-(4-((2-ethylhexyl)oxy)phenyl)-10H-phenoxazine (M2), has not been reported yet. In this report, novel low-bandgap D–A conjugated polymer derivatives including DTDPP, phenothiazine and phenoxazine were successfully synthesized via direct (hetero) arylation polymerization with in the yields of 40.94–60.77%. The obtained D–A conjugated polymers named poly(3,6-Di(2-thienyl)pyrrolo[3,4-c]pyrrole-1,4-dione)-alt-(10-(4-((2-ethylhexyl)oxy) phenyl)-10H-phenothiazine) (P1) and poly(3,6-Di(2-thienyl)pyrrolo[3,4-c]pyrrole-1,4-dione)-alt-(10-(4-((2-ethylhexyl)oxy) phenyl)-10H-phenoxazine) (P2) exhibited a wide range of absorption spectrum in visible light region and have a low bandgaps of 1.4–1.5 eV, as well as thermal stabilities, these D–A conjugated polymers are very promising as activated polymeric materials for organic solar cells (OSCs).