Side-chain engineering has been considered as one of the most promising strategies to optimize non-fullerene acceptors. In this work, we use side-chain engineering to synthesize three fully non-fused electron acceptors (FNEAs) i.e. two symmetric acceptors (4T-BE and 4T-TO) and one asymmetric acceptor (4T-BOE) by different side chain combination onto the tetrathiophene unit, which could effectively tune