Fabricating High‐Performance Organic Solar Cells by Using Inside‐Chain Chlorinated Acceptor as a Ternary Component

Abstract In this study, two molecules, WLA1 and WLA2, with the same molecular backbone but with different degrees of inside‐chain chlorination, are designed and synthesized to elucidate the effects of chlorine substitution strategies on the morphology of small‐molecule acceptors and blended films. The chlorinated WLA2 enhances crystallinity and molecular stacking. For binary organic solar cells (OSCs), the corresponding blended films of WLA2 exhibit suitable phase separation and crystallinity. Therefore, the WLA2‐based binary OSCs achieve a power conversion efficiency (PCE) of 16.80%, which is higher than that of the WLA1‐based binary OSCs (16.21%). In the ternary blending strategy, WLA1 and WLA2 are incorporated into the D18:L8‐BO system as the third component, and the introduction of the chlorinated acceptor WLA2 further improves the crystallinity and facilitates the induction of fiber phase morphology formation. The WLA2‐based ternary OSCs have significantly higher exciton diffusion and charge transport efficiencies compared to L8‐BO and WLA1. The PCE of the WLA2‐based ternary OSCs is 19.64%. This study emphasizes the great potential of combining an inside‐chain chlorinated acceptor molecule with a ternary blending strategy to prepare high‐performance OSCs.