Large energy loss is one of the main limiting factors for power conversion efficiencies (PCEs) of organic solar cells (OSCs). To this effect, the chemical modifications of the famous Y‐series nonfullerene acceptor (NFA) BTP‐4Cl‐BO with a new end group, TPC‐Cl, whose π‐conjugation is extended through the fusing of 3‐(dicyanomethylene)indanone (IC) group with a chlorinated thiophene ring, to synthesize two novel NFAs, BTP‐T‐2Cl and BTP‐T‐3Cl are performed. For BTP‐T‐2Cl with two TPC‐Cl groups, the resulting OSC exhibits a modest PCE of 14.89% but an extraordinary low energy loss of 0.49 eV, because its superior electroluminescence quantum efficiency of 0.0606% mitigates significantly the nonradiative loss (0.191 eV). For BTP‐T‐3Cl with one TPC‐Cl group, the corresponding device shows a higher PCE of 17.61% accompanied by a slightly bigger energy loss of 0.51 eV, which can be ascribed to the optimized morphology and/or efficient charge generation. Furthermore, the ternary OSC adopting two NFAs of BTP‐T‐3Cl and BTP‐4Cl‐BO achieves an impressive PCE of 18.21% (certified value of 17.9%), which is among the highest values for OSCs to date. The above results demonstrate that expanding end groups of NFAs with electron‐donating rings is an effective strategy to realize lower energy losses for OSCs.

To date, the fused-ring electron acceptors show the best photovoltaic performances, and the development of simple non-fullerene acceptors via intramolecular noncovalent interactions can reduce synthetic costs. In this work, four simple non-fullerene acceptors with an A-D-A'-D-A configuration (QCIC1, QCIC2, QCIC3, and QCIC4) were synthesized. They contained the same conjugated backbone (A': quinoxaline; D: cyclopentadithiophene; A: dicyano-indanone) but different halogen atoms and alkyl side chains. Due to the chlorination on the end-groups and the most and/or longest branched alkyl side chains on the backbone, the blended film composed of QCIC3 and donor poly{[2,6'-4,8-di(5-ethylhexylthienyl)benzo [1,2-b : 4,5-b']dithiophene]-alt- [5,5-(1',3'-di-2-thienyl-5',7'-bis(2ethylhexyl)benzo [1',2'-c : 4',5'-c']dithiophene-4,8-dione)]} (PBDB-T) exhibited the strongest π-π stacking and the most suitable phase-separation domains among the four blended films. Therefore, the QCIC3-based organic solar cells yielded the highest power conversion efficiency of 10.55 %. This work provides a pathway to optimize the molecular arrangements and enhance the photovoltaic property of simple electron acceptors through subtle chemical modifications.

The side chains on non-fullerene acceptors (NFAs) can affect greatly the photovoltaic performances of the resulting organic solar cells (OSCs) by regulating the molecular packing and orientation of NFAs. To explore suitable side groups for asymmetric simple NFAs, in this work, we design and synthesize two A-D 1 -A 0 -D 2 -A type NFAs, NTC-4Cl, and PhNTC-4Cl, which own flexible alkyloxy and rigid aryloxy side chains on the A 0 cores, respectively. Due to the same molecular backbone (A 0 : benzotriazole; D 1 : thiophene; D 2 : cyclopentadithiophene; A: dichlorodicyanoindanone), NTC-4Cl and PhNTC-4Cl have similar absorptions and energy levels. However, the PhNTC-4Cl-based OSC gives a higher power conversion efficiency than that of the NTC-4Cl-based one (11.09% vs. 10.82%) because PhNTC-4Cl shows more compact π-π stacking and dominant face-on orientation, enhancing charge transport and mitigating charge recombination. Therefore, this work provides a new insight into the molecular design of high-performance NFAs, especially the rational choice of side groups on asymmetric simple NFAs.

Developing photovoltaic materials well balancing efficiency, stability and cost is highly required for organic solar cells (OSCs) moving toward commercial applications. With such intention, we design two non‐fused ring electron acceptors (NFREAs), 3TT11‐4F and 3TT46‐4F, with large steric hindrance substituents and linear/branched alkyl side chains. The change of alkyl side chains from branched to linear leads to tighter π‐π stacking and uniform molecular orientation for 3TT11‐4F, as revealed in single crystal structure, which further boosts the charge transport and regulates the aggregation property. Thus, a better efficiency of 15.02% is achieved in 3TT11‐4F‐based OSC with significantly improved photocurrent, relative to 3TT46‐4F‐based one (13.79%). Besides, the two NFREAs also enable good device stability with over 70% initial efficiencies maintained after 800 h illumination. Considering the low synthetic complexity, a high i‐FOM value of 16.34% is achieved for 3TT11‐4F‐based OSC, superior to some typical counterparts. Our work provides a good reference for material design with an outstanding figure‐of‐merit.This article is protected by copyright. All rights reserved.