The surface charge properties and local dipole moment of terminal groups have a significant impact on molecular packing and aggregation performance of non-fullerene acceptors (NFAs) for organic solar cells (OSCs). Here, we utilize the interactions between different building blocks within the molecule to regulate the dipole asymmetry of terminal groups by introducing asymmetric inner side chains. Three NFAs, BTA80, BTA81 and BTA82 are designed and synthesized with different substitutions of benzotriazole (BTA)-based inner side chains. The asymmetric introduction of BTA-based inner side chains can modulate the asymmetric surface electrostatic potential and local dipole moments of the terminal groups through the interactions between BTA and the terminal groups, which in turn modifies the molecular orientation and enhances molecular packing. As the result, D18:BTA82-based OSCs achieve the champion power conversion efficiency (PCE) of 17.70% compared to D18:BTA80 and D18:BTA81-based devices with PCE of 16.06% and 16.65%, respectively. Moreover, by introducing the BTA82 as the third component into D18:L8-BO system, the ternary device exhibits a significant improved PCE of 19.60% compared to the device based D18:L8-BO (PCE of 18.73%). This work provides a novel insight into the design of asymmetric NFAs for high performance OSCs.

End-group halogenation strategy in banana-shaped Y-series non-fullerene acceptors (NFAs) play a crucial role in the development of organic solar cells (OSCs). Compared to fluorinated end-groups, chlorinated end-groups offer advantages such as simpler synthesis, lower cost, and higher open-circuit voltage ( V OC). In this study, we replaced the benzothiadiazole (BT) unit in Y-series molecules with an acenaphtho[1,2-b]quinoxaline imide (AQI) structure and utilized IC- p2Cl and IC- o2Cl isomers as end-groups respectively to synthesize two shamrock-shaped NFAs, AQI16 and AQI17. Further investigations revealed that the substitution position of chlorine atoms plays a critical role in modulating the π-π stacking and crystallinity of the materials. Besides, end-group isomerization significantly influences the photophysical and photovoltaic properties of the materials. D18:AQI16 combination achieved an outstanding power conversion efficiency (PCE) of 17.90%, which is obviously higher than that of AQI17 based device (15.14%). This work highlights the impact of isomerization caused by halogen substitution positions on the photovoltaic properties of shamrock-shaped NFAs.