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Enhancing Reverse Intersystem Crossing via Secondary Acceptors: toward Sky-Blue Fluorescent Diodes with 10-Fold Improved External Quantum Efficiency
- Fan, Xuefeng, Li, Chenyu, Wang, Zicheng, Wei, Ying, Duan, Chunbo, Han, Chunmiao, Xu, Hui
- ACS applied materials & interfaces 2019 v.11 no.4 pp. 4185-4192
- diodes, fluorescent dyes, harvesting
- How to simply but effectively facilitate reverse intersystem crossing (RISC) transition is always the key issue for developing high-performance thermally activated delayed fluorescence dyes. In this work, as a proof of concept, a feasible strategy named “acceptor enhancement” is demonstrated with a series of ternary blue emitters (xCzₘPOₙTPTZ) using diphenylphosphine oxide (PO) as secondary acceptors. Compared with its PO-free binary analogue, such a simple introduction of PO groups in pCzPO₂TPTZ dramatically enhances its RISC rate constant (kRISC) by 10 times the level of ∼10⁵ s–¹, accompanied by RISC efficiency (ηRISC) of 92%, which further improves the triplet-to-singlet upconversion for effective triplet harvesting in its devices. As a result, on the basis of a trilayer device structure, pCzPO₂TPTZ realized a state-of-the-art external quantum efficiency beyond 20% with a 10-fold improvement.