Pyrrolo[3,2-b]pyrrole as the Central Core of the Electron Donor for Solution-Processed Organic Solar Cells

A series of three small-molecule acceptor-donor-acceptor (A-D-A) compounds with a tetraaryl-1,4-dihydropyrrolo[3,2-b]pyrrole as the central building block were synthesized and fully characterized. These molecules present high thermal stability and suitable HOMO-LUMO energy levels making them feasible electron-donor materials in bulk heterojunction organic solar cells (BHJ-OSC). Moreover, theoretical work predicts of a lack of planarity and no π-π stacking, furthermore. The electron density of the HOMO is distributed on the pyrrole-pyrrole moiety and that of the LUMO is delocalized, in contrast, on the phenyl groups. The organic solar cells deliver an open-circuit voltage of 0.99 V. However, the overall efficiency is limited due to the low charge mobility measured for holes, 10^-9  cm²  V^-1  s^-1 .