Medium bandgap A–DA′D-A type small molecule acceptors prepared using synergetic modification strategies enable high-performance organic solar cells

Organic solar cells (OSCs) are promising candidates for next-generation photovoltaic technologies due to their inherent advantages of light weight and mechanical flexibility. In recent years, advancements in photovoltaic materials and device fabrication technologies have driven significant improvements in the power conversion efficiency (PCE) of OSCs. Introducing medium-bandgap small molecule acceptors (SMAs) as secondary acceptors into ternary OSCs is an effective strategy to further improve the PCE of OSCs. In this study, we synthesized a series of SMAs Cl24-F, Cl24-H and Cl24-I based on Y6 by employing multiple synergistic modification strategies to expand the molecular bandgap. Among them, Cl24-F yields the highest PCE but exhibits a low open-circuit voltage (V_oc), while Cl24-I suffers from excessive aggregation, leading to poor film morphology. In contrast, Cl24-H features the highest lowest unoccupied molecular orbital energy level (E_LUMO) and the widest bandgap, resulting in a notably high V_oc of 1.01 V in corresponding OSCs. Interaction analyses further confirmed that Cl24-H possesses excellent miscibility with both PM6 donor and BTA-E3 acceptor. Consequently, when Cl24-H was incorporated as a secondary acceptor into the PM6:BTA-E3 system, the PM6:BTA-E3:Cl24-H based ternary OSCs exhibited increased V_oc and short-circuit current density (J_sc), achieving a remarkable PCE of 20.2%. This enhancement is primarily attributed to improved exciton dissociation, balanced charge transport and suppressed carrier recombination enabled by Cl24-H. This work underscores the importance of synthesizing efficient medium-bandgap acceptors and demonstrates their feasibility as third components for boosting OSCs’ performance.