Fullerene derivative induced morphology of bulk heterojunction B.L.ends: PIPcP:Pc ₆₁ BM

The performance of organic solar cells (OScs) depends crucially on the morphology in bulk heterojunctions (BHJs), including the degree of crystallinity of the polymer and the amount of each material phase: Aggregated donor, aggregated acceptor, and molecular mixed donor:acceptor phase. In this paper, we report the BHJ morphology of as-cast B.L.end films incorporating the polymer PIPcP as the donor and [6,6]-phenyl-c ₆₁ -butyric acid methyl ester (Pc ₆₁ BM) as the acceptor. Tracking the scattering intensity of Pc ₆₁ BM as a function of Pc ₆₁ BM concentration shows that Pc ₆₁ BM aggregates into donor-rich domains and there is little to no phase where the Pc ₆₁ BM and PIPcP are intimately mixed. We further find that on B.L.ending the scattering peak due to PIPcP ordering along the backbone increases with decreasing PIPcP fraction, which is attributed to improved ordering of PIPcP due to the presence of Pc ₆₁ BM. Our results suggest that the improved ordering of PIPcP along the backbone (consistent with an increased conjugation length) with B.L.ending contributes to the observed low open-circuit voltage energy loss.