Phosphine Oxide-Balanced Intra- and Inter-Chain Through-Space Charge Transfer in Thermally Activated Delayed Fluorescence Polymers: Beyond 30% External Quantum Efficiency.

Through-space charge transfer (TSCT) is crucial for developing highly efficient thermally activated delayed fluorescence (TADF) polymers. The balance of intra- and inter-chain TSCT can markedly improve the performance, but it is still a big challenge. In this contribution, an effective strategy for "intra- and inter-chain TSCT balance" is demonstrated by a series non-conjugated copolymers containing 9,9-dimethylacridine (DMAC) 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 the balanced intra- and inter-chain TSCT through accurately optimizing inductive and steric effects of the acceptors. DPOT acceptor with the strongest electron-withdrawing ability and the second bigger steric hindrance endows its copolymers with the state-of-the-art photoluminescence and electroluminescence quantum efficiencies beyond 95% and 32%, respectively. It demonstrates that compared to other congeners, the synergistic inductive and steric effects effectively enhance TSCT in DPOT based copolymers for radiation, and suppresses 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. This article is protected by copyright. All rights reserved.