All chlorination strategy on end-group of guest acceptor enables 18.39 % efficiency and high VOC for ternary organic solar cells

The ternary strategy has been proven to be an effective method to improve the power conversion efficiency (PCE) of organic solar cells (OSCs). In this work, a new non-fullerene fused-ring acceptor (BTMe-8Cl) with 3,8-dimethylbenzo[b]benzo[4,5]thieno[2,3-d]thiophene (BTMe) core and all chlorination end-group (4,5,6,7-tetrachloro1H-indene-1,3(2H)-dione) is synthesized and incorporated as a guest electron acceptor in PM6:Y6:BTMe-8Cl ternary system. The addition of BTMe-8Cl effectively improves the open-circuit voltage (VOC) of the ternary OSCs due to the higher lowest unoccupied molecular orbital (LUMO) energy level of BTMe-8Cl than that of Y6. Fine-tuning the proportion of BTMe-8Cl in ternary OSCs results in the optimal phase separations in the ternary films. Finally, an excellent PCE of 18.39 % and a VOC of 0.896 V are achieved for the ternary OSCs based on PM6: Y6:BTMe-8Cl (1:1.2:0.2). Especially, the VOC of 0.896 V is the highest value for PM6:Y6 system up to now.