In situ modulation of the vertical distribution in a blend of P3HT and PC(60)BM via the addition of a composition gradient inducer.

2,2,3,3,4,4,4-Heptafluoro-N-phenyl-butyr-amide (F-ADD) was synthesized and shown to induce a composition gradient in a blend of P3HT and PC60BM. The addition of small amounts (ca. 0.5 wt%) of F-ADD modulated the chemical distribution in the blend along the vertical direction by controlling the blend component interface energy through selective interactions between F-ADD and PC60BM. A homogeneous compositional distribution along the vertical direction in the nanostructured bulk heterojunction (BHJ) increased the interfacial area, which shortened the exciton path length to the donor-acceptor interface and improved the photovoltaic performance.