Synthesis and absorption properties of small-molecule acceptor based rich-electronic benzodiselenophene core with hybrid bromination and fluorination end-group

At present, dihalogenated 1, 1-dicyanomethylene-3-indanone (IC) have attracted widely attention as terminal unit. Here, our work designed and synthesized a new nonfullerene small molecule acceptor material BDSe-FBr, with simultaneously fluorinated and brominated terminal. Due to that bromine atom has more electrons and larger size, and fluorine atom enhanced intermolecular π-πpacking, BDSe-FBr present strong absorption abilities in solution and film. It shows a broad absorption range of 600-800 nm and 700- 900 nm, with the maximum absorption peak in solution and film of 742 nm and 774 nm, respectively, and the optical band gap of BDSe-FBr is 1.40 eV. The results are beneficial for high JSC and less energy loss and these strong absorption abilities are due to that bromine atom has more electrons and larger size, and fluorine atom enhanced intermolecular π-πpacking. The multiple interactions between heteroatom also is beneficial to improve charge transportation and crystallinity. This new A-D-A type small molecules with simultaneously fluorinated and brominated end-group provide an effective strategy to improve photovoltaic performance of acceptor. The introduction of fluorine and bromine atoms simultaneously into the terminal group exhibits great prospects for application in high performance OSCs.