A new acceptor-donor-acceptor (A-D-A) type nonfullerene acceptor, 3TT-FIC, which has three fused thieno[3,2-b]thiophene as the central core and difluoro substituted indanone as the end groups, is designed and synthesized. 3TT-FIC exhibits broad and strong absorption with extended onset absorption to 995 nm and a low optical bandgap of 1.25 eV. The binary device based on 3TT-FIC and the polymer PTB7-Th exhibits a power conversion efficiency (PCE) of 12.21% with a high short circuit current density ( Jsc) of 25.89 mA cm-2. To fine-tune the morphology and make full use of the visible region sunlight, phenyl-C71-butyricacid-methyl ester (PC71BM) is used as the third component to fabricate ternary devices. In contrast to the binary devices, the ternary blend organic solar cells show significantly enhanced EQE ranging from 300 to 700 nm and thus an improved Jsc with a high value of 27.73 mA cm-2. A high PCE with a value of 13.54% is achieved for the ternary devices, which is one of the highest efficiencies in single junction organic solar cells reported to date. The results provide valuable insight for the ternary devices in which the external quantum efficiency (EQE) induced by the third component is evidently observed and directly contributed to the enhancement of the device efficiency.
Keywords: nonfullerene acceptors; organic solar cells; ternary blends.