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

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.