Influence of CN substitution on DPP-furan-based small-molecule acceptors for polymer solar cells

In this study, two small-molecules, p- and o-DPP-F-PhCN, were synthesized via a Suzuki coupling reaction and used as nonfullerene acceptors (NFAs) for poly(3-hexylthiophene) (P3HT)-based polymer solar cells (PSCs). The physical properties of the molecules were examined in terms of the substituent position and the effect of the furan moiety. The introduction of a furan moiety resulted in higher phase-transition temperatures and higher-lying molecular orbital energy levels of the molecules. Substitution at the ortho position also elevated the energy levels of the molecules, resulting in the highest-lying values for o-DPP-F-PhCN. A relatively enhanced and red-shifted UV–vis absorption of o-DPP-F-PhCN indicated its stronger molecular aggregation. PSCs based on two DPP-F-PhCNs exhibited similar device efficiencies. The stronger aggregation behavior of o-DPP-F-PhCN led to a device with a better external quantum efficiency profile; however, the enhanced orbital interactions and resulting stabilized the lowest unoccupied molecular orbital level of o-DPP-F-PhCN led to a relatively low open-circuit voltage.