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

Abstract 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.