Synthesis of 1,6‐ didecylnaphtho [1,2‐ b :5,6‐ b '] difuran‐based copolymers by direct heteroarylation polymerization

The use of direct CH arylation cross‐coupling polymerization was evaluated for the synthesis of donor–acceptor conjugated co‐polymers using the novel donor 1,6‐didecylnaphtho[1,2‐ b :5,6‐ b ']difuran and either thieno[3,4‐ c ]pyrrole‐4,6‐dione (TPD) or 1,4‐diketopyrrolo[3,4‐ c ]pyrrole (DPP) as the acceptor. Thiophene and furan moieties were used to flank the DPP group and the impact of these heterocycles on the polymers' properties was evaluated. The alkyl chains on the diketopyrrolopyrrole monomers were varied to engineer the solubility and morphology of the materials. All of the polymers have similar optoelectronic properties with narrow optical band gaps around 1.3 eV, which is ideal for solar energy harvesting. Unfortunately, these polymers also had high‐lying highest occupied molecular orbital levels of −4.8 to −5.1, and as a result bulk‐heterojunction photovoltaic cells fabricated using the soluble fullerene derivative PC 71 BM as the electron‐acceptor and these polymers as donor materials exhibited poor performance due to limited V oc values. An examination of the films from these blends indicates that film‐thickness and morphology were also a major hindrance to performance and a potential point of improvement for future materials.