Indacenodithiophene‐Based Medium‐Bandgap Guest Acceptor Enables High‐Efficiency Ternary Organic Solar Cells

The ternary organic solar cells (OSCs) have been proven to be an effective strategy for achieving high power conversion efficiency (PCE), exhibiting substantial potential for continuous enhancement of device performance. In this work, a novel nonfullerene acceptor, IDT-FN, is developed utilizing a renowned indacenodithiophene (IDT) core and moderately intense electron-withdrawing terminal groups, serving as the third component in ternary OSCs. IDT-FN demonstrates excellent complementary light absorption and cascaded energy levels with the host materials D18 and CH-6F, resulting in enhanced photon harvesting and charge transport within the ternary blend. Therefore, even the as-cast ternary device manages to surpass the optimal binary host device, achieving a superior PCE of 17.34% compared to the latter's 17.08%. Through optimization, the optimal ternary devices attain an impressive PCE of 18.32%, accompanied by a high open-circuit voltage (Voc) of 0.897 V, a fill factor of 0.745, and a short-circuit current density (Jsc) of 27.41 mA cm-2. This demonstrates a significant success in utilizing IDT-based medium-bandgap guests to achieve state-of-the-art ternary OSCs.