Phosphor-Sensitized Ternary Organic Solar Cells Achieving 18.6% PCE via Ir(III)-Mediated Triplet Energy Transfer and Non-Radiative Recombination Suppression.

Phosphor-sensitized organic solar cells (PS-OSCs) enhance exciton utilization and suppress non-radiative recombination by incorporating triplet-enabled sensitizers into bulk-heterojunction blends. Here, we report a green-emitting Ir-3 complex as a multifunctional phosphor-sensitizer in ternary OSCs based on PM6, two newly designed pyrazine-derived donor polymers, PBDT-Pyz (N1) and PBDT-T-Pyz (N2), and the non-fullerene acceptor L8-BO. N1 and N2 exhibit deep HOMO levels (-5.59/-3.63 eV and -5.58/-3.60 eV) and planar backbones for efficient charge transport, while Ir-3 (Eg opt = 2.50 eV, HOMO/LUMO -5.50/-3.0 eV) functions simultaneously as an interfacial compatibilizer, luminescent-cascade promoter, and triplet-energy mediator. Strong spin-orbit coupling in Ir(III) enables near-quantitative intersystem crossing (ISC), populating long-lived triplet states that undergo rapid triplet-triplet energy transfer (TTET) to L8-BO (Ir-3 T1 = 2.46 eV → L8-BO T1 = 1.85 eV, ΔET1 = 0.61 eV), converting otherwise inaccessible triplet excitons into productive charge generation while suppressing non-radiative voltage loss. The optimized o-xylene-processed PM6:N2:L8-BO device containing 1 wt.% Ir-3 achieved a champion PCE of 18.6%, with Voc of 0.88 V, Jsc of 27.6 mA cm-2, and FF of 76.7%, a 2.6% absolute gain over the binary control. These results establish a combined host-engineering and phosphor-sensitization strategy for high-efficiency, halogen-free, solvent-compatible PS-OSCs.