Low-bandgap non-fullerene acceptors based on selenophene π spacer and alkylated indaceno[1,2-b:5,6-b'] dithiophene for organic solar cells

Three non-fullerene acceptors, i.e. IDT2SeC2C4, IDT2SeC2C4-2F and IDT2SeC2C4-4F, with selenophene pi bridge between central alkylated indaceno[1,2-b: 5,6-b'] dithiophene (IDT) unit and terminal 1,1-dicyano-methylene-3-indanones (ICs) with 0-2 fluorine substituents were synthesized. These molecules presented low optical band gaps in the range of 1.30-1.44 eV. Moreover, compared with the counterparts with phenyl side chains on IDT unit, the alkyl-based molecules achieved higher electron mobility owing to the more ordered and closer p-p stacking. Organic solar cells (OSCs) based on the non-fullerene acceptors were fabricated with the wide band gap polymer PBDB-T as donor. Attributed to the desired morphology with more obvious fibril-like structures, the devices based on IDT2SeC2C4-2F and IDT2SeC2C4-4F with fluorinated IC terminals delivered high power conversion efficiencies (PCEs) over 10%, whereas the devices based on DT2SeC2C4 showed a lower PCE of 8.92%.