A non-fullerene acceptor with all "a" units realizing high open-circuit voltage solution-processed organic photovoltaics

A novel non-fullerene small molecule electron acceptor TTzBT-DCAO, which contains all electron-withdrawing units of 2,1,3-benzothiadiazole, oligothiazole and alkyl cyanoacetate, has been synthesized and characterized. Its photophysical, electrochemical, and photovoltaic properties have been investigated. The material has favorable HOMO and LUMO levels of -5.88 and -3.60 eV, and shows strong absorption in the visible spectrum up to 650 nm. The small molecule:non-fullerene bulk-heterojunction organic photovoltaics (OPVs) were constructed based on two small molecules SF8TBT and TTzBT-DCAO. The influence of the donor:acceptor composition on device performance was investigated. The open-circuit voltages of the devices are over 1.20 V, which is among the highest values reported for single-junction OPVs. The results indicate that small molecules with all electron-withdrawing units could provide a novel route to efficient solution-processed OPVs with high open-circuit voltages.