Dimeric BODIPY Donors Based on the Donor–Acceptor Structure for All-Small-Molecule Organic Solar Cells

Herein, we have designed and synthesized two dimeric BODIPY consisting of a donor–acceptor backbone, in which electron-withdrawing groups of penta-fluorophenyl were introduced at the meso-position of the BODIPY core and different electron-donating groups of triphenylamine (ZMH-3) and carbazole (ZMH-4) groups were introduced at the 3,5-positions of BODIPY moieties. Both ZMH-3 and ZMH-4 showed optical band gaps of 1.49 and 1.39 eV, with deeper highest occupied molecular orbital energy levels of −5.61 and −5.59 eV, respectively. Moreover, the dipole moments of ZMH-3 and ZMH-4, estimated from DFT simulations, are 5.065 and 4.49 D, respectively, indicating that the excitons generated in the ZMH-3 exist with lower binding energy, which is beneficial for the efficient exciton dissociation. Considering these optical and energy levels, we have selected the nonfullerene acceptor ITIC (complementary absorption spectra and suitable energy levels) as the acceptor. After the optimization, the organic solar cells based on ZMH-3 and ZMH-4 attained power conversion efficiencies of about 12.26 and 8.23%, respectively. The enhanced value of power conversion efficiency for the ZMH-3-based OSCs is attributed to the efficient exciton dissociation efficiency, more efficient charge transport and extraction, and suppressed charge recombination.