Fused-ring electron acceptors (FREAs), as a family of non-fullerene acceptors, have achieved tremendous success in pushing the power conversion efficiency of organic solar cells. Here, we reported the detailed molecular packing motifs of two extensively studied FREAs – ITIC and ITIC-Th, which is revealed for the first time the long-range structure ordering along the backbone direction originated from favored end group π-π stacking. The backbone ordering could be significantly enhanced in the ternary film by the mutual mixing of ITIC and ITIC-Th, which gives rise to an improved in-plane electron mobility and better ternary device performance. The backbone ordering might be a common morphological feature of FREAs, providing explanations to previously observed small open circuit voltage loss and superior performance of FREA-based devices and guide the future molecular design of high-performance non-fullerene acceptor.
Manuscript by Mai and Xiao et al. was just accepted by Advanced Materials, 2018, 1802888.