Deep‐Blue OLEDs with BT. 2020 Blue Gamut, External Quantum Efficiency Approaching 40%

Abstract The hyperfluorescence (HF) technology holds great promise for the development of high‐quality organic light‐emitting diodes (OLEDs) for their excellent color purity, high efficiency, and low‐efficiency roll‐off. Sensitizer plays a crucial role in the performance of HF devices. However, designing sensitizers with simultaneous high photoluminescence quantum yield (PLQY), rapid radiative decay (k_r), and fast reverse intersystem crossing rate (k_RISC) poses a great challenge, particularly for the thermally activated delayed fluorescence (TADF) sensitizers targeting deep‐blue HF device. Herein, by introducing a boron‐containing multi‐resonance‐type acceptor into the multi‐tert‐butyl‐carbazole encapsulated benzene molecular skeleton, two TADF emitters featuring hybridized multi‐channel charge‐transfer pathways, including short‐range multi‐resonance, weakened through‐bond, and compact face‐to‐face through‐space charge‐transfer. Benefiting from the rational molecular design, the proof‐of‐concept sensitizers exhibit simultaneous rapid k_r of 5.3 × 10⁷ s⁻¹, fast k_RISC up to 5.9 × 10⁵ s⁻¹, a PQLY of near‐unity, as well as ideal deep‐blue emission in both solution and film. Consequently, the corresponding deep‐blue HF devices not only achieve chromaticity coordinates that fully comply with the latest BT. 2020 standards, but also showcase record‐high maximum external quantum efficiencies nearing 40%, along with suppressed efficiency roll‐off.