Microwave-Assisted Synthesis of Non-Fullerene Acceptors and Their Photovoltaic Studies for High-Performance Organic Solar Cells

This study explores the microwave-assisted cross-coupling methodology to synthesize non-fullerene electron acceptors for solution-processed organic solar cells. Herein, two molecules were designed by introducing the benzo [2,1,3] thiadiazole (BT) unit with a fused aromatic ring leading to an A-A′-D-A′-A (acceptor-acceptor′-donor-acceptor′-acceptor) architecture. The introduction of BT unit stabilizes the resonance structure and enhances the intramolecular charge transfer. The use of a second-generation (G2) palladium catalyst for this direct arylation under microwave irradiation challenges the conventional coupling techniques with yields as good as 80%. This method enables the first report on one-pot coupling of bulky indacenodithienothiophene (IT) core with an electron pulling BT unit. The attachment of dicyanoindanone (ICN) further strengthens the intramolecular charge transfer compared to simple malononitrile (CN). It was found that solar cells based on the ICN terminal group exhibited JSC of 17.54 mA/cm2, VOC of 0.87 V, FF of 73.5, and PCE of 11.1% without additive treatments. This study highlights (1) simple molecular engineering to develop medium band-gap acceptor molecules and (2) microwave-assisted direct arylation - a straightforward strategy to develop the n-type molecular semiconductors in the context of fullerene-free organic solar cells.