Concurrent improvement in JSC and VOC in high-efficiency ternary organic solar cells enabled by a red-absorbing small-molecule acceptor with a high LUMO level

Ternary organic solar cells (OSCs) have demonstrated great potential in promoting the power conversion efficiency (PCE) of single-junction OSCs. Generally, the introduction of a third component with redshifted absorption spectra can broaden the absorption spectra and thereby potentially enhances short-circuit current density (JSC), but reduces open circuit voltage (VOC). Herein, a small-molecule acceptor (SMA) named N7IT with a high LUMO energy level and a redshifted absorption spectrum, is employed as the third component in the PM6:IT-4F-based binary host. Unlike previous results, the introduction of N71T enhances both the VOC and the JSC relative to the PM6:IT-4F host binary system. The champion ternary device (PM6 : IT-4F : N7IT = 1 : 0.7 : 0.3) demonstrates an outstanding PCE of 15.02%, significantly higher than its binary counterparts. This strategy is further validated in PM6:Y6 blends, where the addition of SY3 featuring near-infrared absorption and high LUMO effectively boosts the PCE from 16.49% to 17.07%. Our result proves the effectiveness of an appropriate third component and demonstrates the potential of red-absorbing, high-LUMO SMAs in further promoting the efficiency of single-junction binary OSCs.