Comparison of 3D non-fullerene acceptors for organic photovoltaics based on naphthalene diimide and perylene diimide-substituted 9,9′-bifluorenylidene

Two non-fullerene acceptors (BF-PDI4 and BF-NDI4) have been synthesized by the Suzuki coupling of 2,2',7,7'-tetrakis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9'-bifluorenylidene with 1-bromo-N,N'-di(undecan-6-yl)perylene-3,4:9,10-bis(dicarboximide) (PDI-Br) and 1-bromo-N,N'-dihexylnaphthalene-2,3:6,7-bis(dicarboximide) (NDI-Br), respectively. The photovoltaic performance of BF-PDI4 and BF-NDI4 as acceptors was investigated by fabricating inverted solar cells with structure: ITO/ZnO/active layer/MoO3/Ag. Power-conversion efficiencies of 3.64% and 2.28% were achieved using BF-PDI4 and BF-NDI4 respectively as the acceptor in a blend with the polymer PTB7-Th as a donor. Although BF-PDI4 exhibits much stronger visible absorption than its NDI analogue this absorption makes a relatively small contribution to the photocurrent; however, the photocurrent resulting from polymer absorption in the BF-PDI4 films is larger than that in BF-NDI4-based cells.