Novel low-band gap non-fullerene acceptors based on IDIC core as potential photovoltaic materials

Three novel non-fullerene acceptors (NFAs) (PhBu-IDT-BT-IC, PhBu-IDT-BT-IC4F and PhBu-IDT-BT-IC4Cl) based on 3,8-dioctyl-indaceno[1,2-b:5,6-b’]dithiophene (IDT) core have been designed and synthesized with and without halogen (F and Cl) substitution. The NFAs showed high thermal stability. The ultraviolet–visible absorption studies in solution and thin film for the three acceptors revealed maximum absorption from 687 to 732 nm and 731 to 847 nm, respectively. The onset of absorption in the thin film was found to be extending up to around 960 nm for PhBu-IDT-BT-IC4Cl. The optical band gap ranged from 1.30 to 1.41 eV, which are very low and useful for photovoltaic application. The introduction of halogen appreciably altered the LUMO energy levels, whereas the HOMO energy levels were nearly intact. These small molecule non-fullerene acceptors could be used as potential acceptors in bulk heterojunction organic photovoltaic (BHJ-OPV) applications.