Ternary Blend Organic Photovoltaics with High Efficiency and Stability Through Energy Transfer and Molecular Packing Induced by an A-D-A Small Molecule.

A novel A-D-A type small molecule (DTP-2EH-IO2Cl) incorporating dithiophenepyrrole (DTP) core with indene-dione (IO2Cl) side chain with an intermediate band gap and rigid structure is incorporated into polymer donor PM6 and one of the three A-DA'D-A small molecule acceptor-L8-BO, BTP-eC9 or Y6-for ternary-blend organic photovoltaics (OPVs). The third component DTP-2EH-IO2Cl induces not only energy transfer but also stronger molecular packing of the acceptors, resulting in a larger coherence length and enhanced absorption that enhances devices' power conversion efficiencies (PCE) and thermal stability. The PCE values of the champion ternary-blend devices PM6:L8-BO, PM6:BTP-eC9, and PM6:Y6 incorporating DTP-2EH-IO2Cl are 19.2, 18.3, and 17.6%, respectively, versus 16.5, 15.8, and 15.4% for their corresponding binary blend devices, displaying relative increases from 14 to 16%. The thermal stability (T80) of the PM6:L8-BO: DTP-2EH-IO2Cl ternary blend device increases dramatically to 568 h from 57 h for the PM6:L8-BO binary blend device. These enhancements can be attributed to the effectiveness of the A-D-A type rigid DTP-2EH-IO2Cl as the third component in increasing light absorption through energy transfer and inducing intermolecular packing to the A-DA'D-A acceptors, providing an effective way to tune the morphology and to boost both the PCE and thermal stability of OPVs.