5H-Fluoreno [3,2-b:6,7-b'] Dithiophene Based Non-fullerene Small Molecular Acceptors for Polymer Solar Cell Application

Two novel non-fullerene small molecule acceptors were prepared with the conjugated backbone of 5H-fluoreno[ 3,2-b:6,7-b']dithiophene carrying the electron deficient unit of dicyanomethylene indanone (DICTFDT) and rhodanine (TFDTBR), respectively. The two acceptors exhibited excellent thermal stability and strong absorption in the visible region. The LUMO level is estimated to be at -3.89 eV for DICTFDT and -3.77 eV for TFDTBR. When utilized as the acceptor in bulk heterojunction polymer solar cells with the polymer donor of PBT7-Th, the optimized maximum power conversion efficiency of 5.12% and 3.95% was obtained for the device with DICTFDT and TFDTBR, respectively. The research demonstrates that 5H-fluoreno[3,2-b:6,7-b']dithiophene can be an appealing candidate for constructing small molecular electron acceptor towards efficient polymer:non-fullerene bulk heterojunction solar cells.