High-Performance Non-Fullerene Acceptor Derived from Diathiafulvalene Wings for Solution-Processed Organic Photovoltaics

A solution-processable small-molecule nonfullerene electron acceptor BAF-2HDT (7,7′-(9,9-didecyl-9H-fluorene-2,7-diyl)bis(4-((4,5-bis(hexylthio)-1,3-dithiol-2 ylidene)methyl)benzo[c][1,2,5]thiadiazole) bearing hexadiathiafulvalene (HDT) wings as end groups has been synthesized for bulk heterojunction organic photovoltaics. The molecule shows broad absorption in the 300–600 nm range with a molar extinction coefficient (e) of 9.32 × 104 M–1·cm–1 exceeding to that of [6,6]-phenyl-C71-butyric acid methyl ester of 2.8 × 104 M–1·cm–1 at 461 nm. The HOMO and LUMO energy levels of the molecule are found to be −5.69 and −3.58 eV, respectively which is compatible with low band gap high-performance polymers such as poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di(2-octyldodecyl)-2,2′;5′,2″;5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD). Photoluminescence-quenching measurements confirm that the molecule BAF-2HDT has excellent electron-accepting capability. The organic solar cells made from BAF-2HDT ble...