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.