Central Molecular Stacking Regulator Boosts the Efficiency of Organic Solar Cells

Abstract Central unit engineering in non‐fullerene acceptors (NFAs) plays a pivotal role in regulating molecular stacking, and further greatly affects the power conversion efficiency (PCE) of organic solar cells (OSCs). A high‐efficiency NFA of CS4 is developed in this work, with a sulfur‐bridged and chlorinated phenyl group on the central unit as a molecular stacking regulator. Detailed analyses reveal that CS4 exhibits tighter molecular packing, more balanced charge mobility, superior phase separation, and reduced energetic disorder compared to its counterpart, CH3. As a result, a notable efficiency of 18.57% is observed in the D18:CS4‐based binary OSC, much higher than 17.81% for that of CH3. Moreover, D18:CS4:BTP‐eC9‐based ternary device renders a champion PCE of 20.16%. D18:CS4 and ternary devices exhibit enhanced stability over D18:CH3. Under the pressure of 65 °C, T 80 lifetimes are 1200 h for D18:CS4 and 2500 h for D18:CS4:BTP‐eC9‐based ternary device. Under continuous light illumination, T 80 reaches 550 and 710 h, respectively. This study demonstrates an effective strategy to boost high‐performance OSCs through precise design of central molecular stacking regulator.