Phase behavior of π-conjugated polymer and non-fullerene acceptor (PTB7-Th:ITIC) solutions and blends

Phase diagrams of ternary pi-bonded polymer (PTB7-Th) solutions were constructed as a function of molecular weight, temperature, and electron acceptor species (ITIC, PC61BM and PC71BM). For this purpose, the Flory-Huggins lattice theory was employed with a constant chi interaction parameter, describing a binodal, spinodal, tie line, and critical point. Then, the morphologies of the blends composed of highly disordered PTB7-Th and crystallizable ITIC were investigated by atomic force microscopy. Subsequently, the surface polarities of the PTB7-Th:ITIC thin films were examined by water contact-angle goniometer, exhibiting a transition at the composition of similar to 60 +/- 10 wt.% ITIC. Furthermore, X-ray diffraction indicated the presence of ITIC's crystallites at >= 70 wt.% ITIC. Hence, the PTB7-Th:ITIC system was observed to undergo a phase transition at similar to 60-70 wt.% ITIC.

Automated summary

Phase diagrams of ternary pi-bonded polymer (PTB7-Th) solutions were constructed to investigate the effects of molecular weight, temperature, and electron acceptor species on the solution properties. The morphologies and surface properties of blends composed of PTB7-Th and ITIC were examined using atomic force microscopy and water contact-angle goniometer. The results revealed a phase transition in the PTB7-Th:ITIC system at around 60-70 wt.% ITIC.