Hidden Structure Ordering Along Backbone of Fused‐Ring Electron Acceptors Enhanced by Ternary Bulk Heterojunction

Fused‐ring electron acceptors (FREAs), as a family of non‐fullerene (NF) acceptors, have achieved tremendous success in pushing the power conversion efficiency of organic solar cells. Here, the detailed molecular packing motifs of two extensively studied FREAs—ITIC and ITIC‐Th are reported. It 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 guiding the future molecular design of high‐performance NF acceptors. The existence of the long‐range backbone ordering in films based on fused‐ring electron acceptors—ITIC and ITIC‐Th—is revealed. The backbone ordering, originated from the favored end group π–π stacking, could be significantly enhanced in the ternary PBDB‐T:ITIC:ITIC‐Th film and results in improved in‐plane electron mobility and device performance.