Asymmetric Local Dipole of Terminal Groups Enabled by Asymmetric Aromatic Side Chains for High‐Performance Organic Solar Cells

Comprehensive Summary 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.