Small Singlet–Triplet Gap Terpolymer Donor with a Simple Pt Complex Enables Organic Solar Cells with Low Energy Loss and Over 19.2% Efficiency

Abstract Suppressing the non‐radiative loss in the organic solar cells (OSCs) through molecular design remains a significant challenge. Typically, triplet state of organic semiconductors is lower than the charge transfer (CT) state, contributing to substantial non‐radiative loss via the triplet state. Herein, a set of terpolymers is prepared by introducing a simple Pt complex block into the PM6 polymer backbone. These metalated terpolymers exhibit high triplet energy ( E T1 ) and small singlet–triplet energy gap (∆ E ST ), facilitating fast intersystem crossing (ISC) process to generate triplet excitons. Consequently, the metalated terpolymers show enhanced exciton lifetime and diffusion length, and most importantly, effectively suppress the non‐radiative recombination via terminal triplet loss channels. Moreover, the Pt complex modifies the molecular aggregation of the polymer, hence optimizing the morphology of the active blends. The PM6‐Pt1:L8‐BO devices achieve a champion power conversion efficiency (PCE) of 18.54% (certified as 18.32%), the highest reported for metalated terpolymers to date. The PCE is further increased to a record high 19.24% in the PM6‐Pt1:PM6:L8‐BO (0.8:0.2:1.2, wt/wt/wt) ternary devices. Overall, this work provides a feasible approach to designing terpolymers with high E T1 , thereby reducing non‐radiative loss in the OSCs.