Improving the performances of all-small-molecule organic solar cells by fine-tuning halogen substituents of donor molecule

Abstract

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. • A new small molecular donor named DRTB-CT with two chlorinated side chains was synthesized. • DRTB-CT exhibits better photoelectric properties compared with fluorinated counterpart. • The steric effect of large radius prevents the excessive self-aggregation in donor phases. • DRTB-CT based all-small-molecule organic solar cells gave a high PCE of 9.05%. • Introduction of chlorine atoms is favorable for designing new materials with high performances.