Triarylboron-based TADF emitters with perfluoro substituents: high-efficiency OLEDs with a power efficiency over 100 lm W −1

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2020-01, Vol.8 (12), p.4253-4263
• Main Authors: Kumar, Ajay, Lee, Woochan, Lee, Taehwan, Jung, Jaehoon, Yoo, Seunghyup, Lee, Min Hyung
• Format: Article
• Language: English
• Subjects: Boron; Carbazoles; Crystal structure; Crystallography; Efficiency; Electric potential; Electroluminescence; Emitters; Fluorescence; Organic light emitting diodes; Perfluoro compounds; Perfluoroalkyl & polyfluoroalkyl substances; Photoluminescence; Power efficiency; Power management; Quantum efficiency; Substitutes; Toluene; Voltage
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/C9TC06204A

We report boron-based thermally activated delayed fluorescence (TADF) emitters that can lead to high-efficiency organic light-emitting diodes (OLEDs) with high power efficiency and low driving voltage. ortho -Carbazole-appended triarylboron compounds ( 2–7 ), in which perfluoroalkyl (CF 3 and C 3 F 7 ) or perfluoroaryl (4-CF 3 C 6 F 4 ) groups are attached as secondary acceptors, are prepared and characterized. The compounds exhibit a light greenish to yellow emission in toluene with high photoluminescence quantum yields up to 100%. The twisted donor (D)–acceptor (A) structure, as evidenced by both the X-ray crystal structures and theoretically optimized structures, leads to a small energy splitting (Δ E ST < 0.1 eV) between the excited singlet and triplet states, giving rise to strong TADF. High-efficiency TADF-OLEDs are realized with the CF 3 - and 4-CF 3 C 6 F 4 -substituted compounds as emitters. The optimized OLEDs based on the CF 3 -substituted emitter ( 5 ) show a high external quantum efficiency of 29.9% with a low turn-on voltage of 2.35 V. In particular, the devices achieve an ultrahigh power efficiency (PE) of 123.9 lm W −1 without any light-outcoupling enhancement, which is among the best PE values for the reported TADF-OLEDs. The devices also maintain a high PE at the practical brightness, such as 100 cd m −2 (118.7 lm W −1 ) and 1000 cd m −2 (82.3 lm W −1 ).