High-Performance Ternary Organic Photovoltaics Incorporating Small-Molecule Acceptors with an Unfused-Ring Core

Organic photovoltaics (OPVs) have made enormous progress in recent years, benefiting from the rapid development of non-fullerene acceptors (NFAs). Most high-performance NFAs, however, have featured π-conjugated backbones with large-fused core structures, increasing the complexity and cost of their synthesis and limiting their practical commercialization. In this study, we synthesized a series of acceptor–donor–acceptor-configured small-molecule acceptors (NTCPDTCN, NTCPDTID, and NTCPDT2F) based on a core structure featuring a naphthobisthiadiazole (NT) group and two cyclopenta[2,1-b,3,4-b′]dithiophene (CPDT) groups as the unfused-ring central unit and equipping malononitrile (CN), 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (ID), and 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (2F) groups as terminal groups. When blended with PM7, the NTCPDTCN-containing binary device displayed a high open-circuit voltage (VOC) of 1.04 V, without self-aggregation, as well as the best device performance. When blended with PM6:Y6, the ternary NTCPDTCN-, NTCPDTID-, and NTCPDT2F-based OPVs provided power conversion efficiencies of 15.4 ± 0.09, 14.6 ± 0.15, and 16.0 ± 0.08%, respectively. NTCPDT2F provided complementary absorption and allowed fine-tuning of the blend morphology, resulting in suppression of charge recombination and improvements in charge generation and collection, thereby achieving the highest device performance. Thus, our findings might provide some directions for developing high-performance ternary OPVs through the introduction of unfused-ring small-molecule acceptors