A new acceptor-donor-acceptor (A-D-A) type small molecular donor named as DRTB-CT was designed and synthesized by replacing the fluorine atoms of DRTB-FT with chlorine atoms. Such a small change plays an important role in inhibiting the strong molecular crystallinity and excessive self-aggregation in donor phase due to the larger radius of chlorine atom, which leads to optimized morphology of the active layer. Based on the same nonfullerene acceptor (F-2Cl), the optimal device of DRTB-CT exhibits a higher power conversion efficiency (PCE) of 9.05% compared with that of the fluorinated molecule (7.66%), benefiting from the increased fill factor (FF, 0.568) and short-circuit current density (J(sc), 15.07 mA cm(-2)). The results indicate that the introduction of chlorine atoms is an effective strategy in developing new small molecular donors with high device performances.