Star-Shaped Fused-Ring Electron Acceptors with a C3h-Symmetric and Electron-Rich Benzotri(cyclopentadithiophene) Core for Efficient Nonfullerene Organic Solar Cells

Classical fused-ring electron acceptors (FREAs) with linear acceptor-donor-acceptor (A-D-A) architecture continuously break records of power conversion efficiency (PCE) in nonfullerene organic solar cells. In contrast, the development of star-shaped FREAs still lags behind. Herein, a new C3h-symmetric and electron-rich core, benzotri(cyclopentadithiophene) (BTCDT) in which the central benzo[1,2-b:3,4-b’:5,6-b”]trithiophene fused with three outer thiophenes via three cyclopentadienyl rings, are synthesized and used for the construction of star-shaped FREAs (BTCDT-IC and BTCDT-ICF). Owing to the strong electron-donating ability of BTCDT unit, both acceptors exhibit the effective intramolecular charge transfer, leading to the strong absorption in the region of 500-800 nm with narrow bandgaps below 1.70 eV as well as suitable highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels. Comparing with non-fluorinated BTCDT-IC, fluorinated BTCDT-ICF red-shifts the absorption ...