Dimeric BODIPY Donors\nBased on the Donor–Acceptor\nStructure for All-Small-Molecule Organic Solar Cells

Herein, we have designed and synthesized two dimeric\nBODIPY consisting\nof a donor–acceptor backbone, in which electron-withdrawing\ngroups of penta-fluorophenyl were introduced at the <i>meso</i>-position of the BODIPY core and different electron-donating groups\nof triphenylamine (<b>ZMH-3</b>) and carbazole (<b>ZMH-4</b>) groups were introduced at the 3,5-positions of BODIPY moieties.\nBoth <b>ZMH-3</b> and <b>ZMH-4</b> showed optical band\ngaps of 1.49 and 1.39 eV, with deeper highest occupied molecular orbital\nenergy levels of −5.61 and −5.59 eV, respectively. Moreover,\nthe dipole moments of <b>ZMH-3</b> and <b>ZMH-4</b>, estimated\nfrom DFT simulations, are 5.065 and 4.49 D, respectively, indicating\nthat the excitons generated in the <b>ZMH-3</b> exist with lower\nbinding energy, which is beneficial for the efficient exciton dissociation.\nConsidering these optical and energy levels, we have selected the\nnonfullerene acceptor ITIC (complementary absorption spectra and suitable\nenergy levels) as the acceptor. After the optimization, the organic\nsolar cells based on <b>ZMH-3</b> and <b>ZMH-4</b> attained\npower conversion efficiencies of about 12.26 and 8.23%, respectively.\nThe enhanced value of power conversion efficiency for the <b>ZMH-3-</b>based OSCs is attributed to the efficient exciton dissociation efficiency,\nmore efficient charge transport and extraction, and suppressed charge\nrecombination.