A 9,9′-spirobi[9H-fluorene]-cored perylenediimide derivative and its application in organic solar cells as a non-fullerene acceptor

A structurally non-planar molecule (SBF-PDI4) with a 9,9'-spirobi[9H-fluorene] (SBF) core and four perylenediimides (PDIs) at the periphery was designed, synthesized and characterized. This compound shows a low-lying LUMO energy level of -4.11 eV, which is similar to that of PCBM, but with intensive light absorption ability in the range 450-550 nm. A high power conversion efficiency (PCE) of 5.34% was obtained for a solution processed bulk heterojunction solar cell (BHJSC) using SBF-PDI4 as the electron acceptor and a low-band gap polymer poly[[4,8-bis[5-(2-ethylhexyl)thiophene-2-yl]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7-Th) as the electron donor. These results demonstrate that PDI derivatives with a three dimensional molecular structure could serve as high performance electron acceptors in BHJSCs.