Fully non-fused electron acceptors (FNEAs) have shown a promising prospect for commercial applications of organic solar cells (OSCs) due to their simple structures and low costs. Herein, two terthiophene-based NFEAs 3T-1 and 3T-2 were exploited from a single thiophene ring as the starting material. Octyl substituted 3T-1 exhibits strong crystallinity, poor miscibility, and forms large aggregates when blending with polymer D18, leading to an inferior power conversion efficiency (PCE). While 2-ethylhexyl substituted 3T-2 possesses good solubility and enhanced compatibility with polymer D18, the blend film exhibits an appropriate morphology, face-on molecular orientation, and efficient charge transport. As a result, the as-cast device based on 3T-2 exhibits a significantly enhanced PCE of 11.12% processed by non-halogenated o-xylene as the solvent, which is the highest value of terthiophene based FNEAs for OSCs so far. Our work provides insight into molecular design of FNEAs for high-performance OSCs.