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

A series of three acceptor-donor-acceptor (A-D-A) small molecules using a tetraaryl-1,4-dihydropyrrolo[3,2-b]pyrrole in their 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 was also performed obtaining a prediction of a lack of planarity and no p-p stacking, furthermore, the probability of the Highest Occupied Molecular Orbital (HOMO) is distributed on the pyrrole-pyrrole moiety and the probability of the Lowest Unoccupied Molecular Orbital (LUMO) is delocalized, on the contrary, on the phenyl groups. The organic solar cells deliver an open-circuit voltage of 0.99V. However, the overall efficiency is limited due to the low charge mobility measured for holes, 10-9 cm2V-1s-1.