Fused-Ring Nonfullerene Acceptor Forming Interpenetrating J-Architecture for Fullerene-Free Polymer Solar Cells

An interesting and important question emerges with the rapid advances of the highly efficient fused-ring nonfullerene acceptors; that is, how the acceptor molecules form aggregates in its blended film with a donor polymer/small molecule so as to offer highly efficient exciton diffusion and electron transport? To answer this question, a new acceptor molecule, 3,9-bis(5-methylene-4-one-6-(1,1-dicyanomethylene)-cyclopenta[c]thiophen-2,8-dimethyl)-5,5,11,11-tetrakis(4-n-hexylphenyl)-dithieno[2,3-d:2', 3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (ITCT-DM), is designed and synthesized herein and its unique interpenetrating J-architecture is presented in which the acceptor molecules form compacted and displaced pp-stacks with the distances of 3.1-4.2 angstrom. Again the crystal structure data are correlated with the grazing-incidence X-ray diffraction (GIXRD) data of the pure acceptor and its polymer: acceptor blended films, which gives a clearer picture about the origins of the acceptor's GIXRD signals in both the pure and its blended films. Again, these results unveil the key roles of the uses of 1,8-diiodooctane (DIO) and thermal annealing treatment in optimizing the acceptor phase morphologies in the donor: acceptor blended film, and the combination of the thermal annealing and DIO treatment leads to obtain higher crystallinity for both the donor and acceptor phases, more compacted packing, and finer morphologies. A power conversion efficiency of 10.5% is obtained.