Realizing Stable High‐Performance and Low‐Energy‐Loss Ternary Photovoltaics through Judicious Selection of the Third Component

The ternary strategy can be used to optimize the light harvesting (i.e., complementary absorption), energy level alignment, and blend morphology of organic photovoltaics (OPVs). Herein, ZY‐4Cl is chosen as the third component in a PM6:Y6‐based OPV. ZY‐4Cl has a small highest occupied molecular orbital (HOMO) energy level offset with Y6 (0.02 eV) and a small lowest unoccupied molecular orbital (LUMO) energy level offset with PM6 (0.06 eV), and provided low energy loss of 0.538 eV for the resulting ternary OPV. Furthermore, the system displayed complementary absorption and a suitable value of χ_{PM6–ZY‐4Cl,} and the similar chemical structures of ZY‐4Cl and Y6 assured their great miscibility. The embedding of ZY‐4Cl improved the light harvesting, blend morphology, exciton dissociation, bimolecular/trap‐assisted recombination, and long‐term stability when comparing the ternary OPV with the PM6:Y6‐based binary OPV. Consequently, the power conversion efficiency (PCE) increased from 15.5 ± 0.22% for the binary OPV to 17.1 ± 0.23% for the ternary OPV, with the best PCE reaching 17.6%. The unencapsulated ternary OPV exhibited excellent air stability, maintaining 94% of its initial PCE for over 1390 h (25 °C, 40% humidity). This study provides a useful strategy for selecting the third component to improve the OPV performance.