Fig. 2. Chemical structures, optical data and device performances of materials used. (A) Chemical structures of PffBT4T-2DT and acceptors used in this study. (B) Normalized UV-vis absorption spectra of neat films. (C) Energy level diagram for the donor and acceptor materials obtained from film CV measurements. EA of PffBT4T-2DT and IP of acceptors are estimated from the optical bandgaps of the materials. (D) Current–voltage curves of PffBT4T-2DT:FBR devices compared with PffBT4T-2DT:PCBM under illumination of 100 mW cm^–2.