Design of Halogenated Donors for Efficient All-Small-Molecular Organic Solar Cells

Precise adjustment of the nanoscale morphology within the active layers is crucial for optimizing the photovoltaic performance of all-small-molecule organic solar cells (ASM-OSCs), and the halogen substituent strategy for photovoltaic materials plays a vital role in the development of the morphology evolution. In this work, we systematically study a series of acceptor–donor–acceptor (A-D-A) type small-molecule donors by incorporating halogenation at the thienyl benzo[1,2-b:4,5-b′]dithiophene (BDT-T) donor core unit named BSTR-F, BSTR-Cl, and BSTR-Br. Such halogenation is demonstrated to induce a significant increase in the ionization potential, i.e., deeper HOMO, and more ordered packing property. Using N3 as the acceptor, the BSTR-F-based devices achieve a power conversion efficiency (PCE) up to 15.93%, compared with the control nonhalogenated donor BSTR-H-based devices of 13.80%, indicating that the suitable halogenation strategy could effectively promote the high performance of ASM-OSCs.