Phosphine‐Oxide‐Balanced Intra‐ and Interchain Through‐Space Charge Transfer in Thermally Activated Delayed Fluorescence Polymers: Beyond 30% External Quantum Efficiency

Abstract Through‐space charge transfer (TSCT) is crucial for developing highly efficient thermally activated delayed fluorescence polymers. The balance of intra‐ and interchain TSCT can markedly improve performance, but it is still a big challenge. In this work, an effective strategy for “intra‐ and interchain TSCT balance” is demonstrated by way of a series of non‐conjugated copolymers containing a 9,9‐dimethylacridine donor and triazine‐phosphine oxide (PO)‐based acceptors. Steady‐state and transient emission spectra indicate that compared to the corresponding blends, the copolymers can indeed achieve balanced intra‐ and interchain TSCT by accurately optimizing the inductive and steric effects of the acceptors. The DPOT acceptor with the strongest electron‐withdrawing ability and the second bigger steric hindrance endows its copolymers with state‐of‐the‐art photoluminescence and electroluminescence quantum efficiencies beyond 95% and 32%, respectively. This demonstrates that, compared to other congeners, the synergistic inductive and steric effects effectively enhance TSCT in DPOT‐based copolymers for radiation, and suppress singlet and triplet quenching. The record‐high efficiencies of its devices make this kind of copolymers hold the potential for low‐cost, large‐scale, and high‐efficiency applications.