Effect of terminal fluorination of indenoindene-cored non-fullerene molecular acceptors for photovoltaic application

Abstract

Two new non-fullerene molecule acceptors (NFAs), IDTIC and IDTIC-4F, based on a 5,10-dihydroindeno[2,1-a]indene core and 4H-cyclopenta[1,2-b:5,4-b']dithiophene (CPDT) bridges, were designed and synthesized. The fluorine-terminated IDTIC-4F shows a larger bathochromic shift than the non-fluorinated IDTIC. When blending with a PBDB-T polymer donor to fabricate organic solar cells, the IDTIC and IDTIC-4F acceptors respectively showed power conversion efficiencies (PCEs) of 5.60% and 6.77%. The PBDB-T:IDTIC-4F device performed better on Jsc and FF, which was attributed to the morphological evolution due to terminal fluorinated design of NFAs. Comparatively, the terminal fluorinated IDTIC-4F contributes to the formation of a more uniform film with less traps, which improves the charge transport and reduces the bimolecular recombination within the device. The work demonstrates that terminal fluorination of NFAs is an efficient design to modifying the morphology and performance of non-fullerene organic photovoltaics.