Synthesis and characterization of diketopyrrolopyrrole‐based conjugated polymer with biphenyl for organic photovoltaic cells

Abstract Designing a moderate band gap is sometimes intentionally chosen. When the donor polymer has a deeper HOMO level, a higher Voc can be gained which boosts total PCE in organic photovoltaics ( OPVs ) (Liao et al., Joule 2020 , 4 (1), 189–206; Mamba et al., J. Phys. Chem. A 2021 , 125 (50), 10593–10603; Choi and Jo, Org. Electron. 2013 , 14 (6), 1621–1628; Jo et al., Org. Electron. 2012 , 13 (10), 2185–2191). This is crucial in DPP ‐based copolymer frameworks, which frequently have short band gaps and may experience poor Voc. Since DPP is a low bandgap due to strong‐acceptor, thus, modifying it with weak donor units can raise the bandgap and lower the HOMO to make it suitable for multi‐junctions or higher Voc. We report the synthesis, properties, and photovoltaic applications of a donor‐acceptor (D‐A) conjugated copolymer based on diketopyrrolopyrrole ( DPP ) and biphenyl, namely PDDPPhenyl . This polymer exhibits broad absorption ranging from 400 to 900 nm with a band gap of 1.59 eV . As expected, a low HOMO level of −5.29 was gained by introducing biphenyl as a weaker donor. The optimized weight ratio goes to 1:4 for PDPPPhenyl : PC 71 BM with 3.8% PCE .