Non-fullerene acceptors with alkoxy side chains and different halogenated end groups for efficient organic solar cells

Abstract

Two polycyclic non-fullerene acceptors BTMe-OEH-2F and BTMe-OEH-2Cl were constructed by connecting the fused ring core with 4-(2-ethylhexyloxy) phenyl side chain to two kind of end groups 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile (2F-IC) and 2-(5,6-dichloro-3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile (2Cl-IC), respectively. Compared with BTMe-OEH-2F, BTMe-OEH-2Cl showed a more red-shifted absorption and lower energy level. When the two non-fullerene acceptors were blended with the donor PM6, a fiber distribution and continuous nanophase separation can be observed in the PM6:BTMe-OEH-2Cl blend film, and more balanced charge transport and less charge recombination were exhibited in the organic solar cell (OSC) device based on BTMe-OEH-2Cl, which achieved a higher PCE of 13.23% with a Voc of 0.98 V, a Jsc of 18.76 mA cm−2 and a FF of 72.23%. These results proved that the synergistic effect between side chains and end groups on the properties of fused-ring electron acceptors (FREAs) can be exerted by choosing appropriate end groups to match with alkoxy side chains.