Asymmetric non-fullerene acceptor based on a cyclohexane side chain for efficient organic solar cell

Symmetry variation has been recognized as a simple but effective strategy to fine-tune the properties of small molecular acceptors (SMAs), thus enhancing the power conversion efficiency (PCE) of organic solar cells (OSCs). Here, a new asymmetric SMAs of Y6-sch with a cyclohexane side chain and an iso-alkyl side chain was synthesized, and the photovoltaic performance was compared with its counterpart that with two cyclohexane side chains (Y6-dch). Using PM6 as polymer donor, asymmetric Y6-sch obtained an efficient PCE of 16.01% with an open-circuit voltage (Voc) of 0.859 V, a short-circuit current (Jsc) of 25.46 mA cm−2, and a fill factor (FF) of 73.20%, which is much higher than that of the symmetric SMA Y6-dch based devices (14.19%). The higher device performance for PM6: Y6-sch is a combined result of improved Voc and Jsc, due to the joint contributions of its more matched energy levels, efficient exciton charge separation, higher charge mobilities, and less exciton recombination. In addition, because of better miscibility, the active layer based on PM6: Y6-sch obtains a better morphology. Our results indicate symmetric approach with cyclohexane side chain could provide a useful approach for the design of high performance asymmetric SMAs.