Abstract
We report an efficient deep-blue organic light-emitting diode (OLED) based on a heptazine-based thermally activated delayed fluorescent (TADF) emitter, 2,5,8-tris(diphenylamine)-tri-s-triazine (HAP-3DPA). The deep-blue-emitting compound, HAP-3DPA, was designed and synthesized by combining the relatively rigid electron-accepting heptazine core with three electron-donating diphenylamine units. Due to the rigid molecular structure and intramolecular charge transfer characteristics, HAP-3DPA in solid state presented a high photoluminescence quantum yield of 67.0% and obvious TADF nature with a short delayed fluorescent lifetime of 1.1 μs. Most importantly, an OLED incorporating HAP-3DPA exhibited deep-blue emission with Commission Internationale de l’Eclairage (CIE) coordinates of (0.16, 0.13), a peak luminance of 10,523 cd/m−2, and a rather high external quantum efficiency of 12.5% without any light out-coupling enhancement. This finding not only reports an efficient deep-blue TADF molecule, but also presents a feasible pathway to construct high-performance deep-blue emitters and devices based on the heptazine skeleton.
Highlights
Considerable progress in organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) has triggered intensive effort to develop highperformance pure organic electroluminescent (EL) materials over the past decade [1,2,3,4,5]
As the third generation of organic light-emitting materials in comparison with traditional fluorescent and phosphorescent materials, TADF emitters can harvest both singlet and triplet excitons without the use of noble metals, which are considered as the promising option for next-generation OLEDs with numerous features, such as high efficiency, metal-free, diverse molecular design, and low cost [6,7,8]
A large number of blue TADF emitters have been developed, whereas most of them belong to the sky-blue region [10,11,12,13,14,15,16,17]
Summary
Considerable progress in organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) has triggered intensive effort to develop highperformance pure organic electroluminescent (EL) materials over the past decade [1,2,3,4,5]. As the third generation of organic light-emitting materials in comparison with traditional fluorescent and phosphorescent materials, TADF emitters can harvest both singlet and triplet excitons without the use of noble metals, which are considered as the promising option for next-generation OLEDs with numerous features, such as high efficiency, metal-free, diverse molecular design, and low cost [6,7,8]. In order to obtain a small ∆EST and efficient TADF emitters, molecules featuring electron donor-acceptor strcutures are very popular and effective. To the best of our knowledge, several highly efficient heptazine-based red and green TADF emitters have been reported [22,23,24,25], while there are no published heptazine-based blue or deep-blue TADF emitters
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