Improved stability of blue TADF organic electroluminescent diodes via OXD-7 based mixed host

Abstract

Thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) have been demonstrated in applications such as displays and solid-state lightings. However, weak stability and inefficient emission of blue TADF OLEDs are two key bottlenecks limiting the development of solution processable displays and white light sources. This work presents a solution-processed OLED using a blue-emitting TADF small molecule bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS) as an emitter. We comparatively investigated the effects of single host poly(N-vinylcarbazole) (PVK) and a co-host of 60% PVK and 30% 2,2′-(1,3-phenylene)-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole] (OXD-7) on the device performance (the last 10% is emitter DMAC-DPS). The co-host device shows lower turn-on voltage, similar maximum luminance, and much slower external quantum efficiency (EQE) roll-off. In other words, device stability improved by doping OXD-7 into PVK, and the device impedance simultaneously and significantly reduced from 8.6 × 10³ to 4.2 × 10³ W at 1000 Hz. Finally, the electroluminescent stability of the co-host device was significantly enhanced by adjusting the annealing temperature.

Graphical abstract

Keywords

blue thermally activated delayed fluorescence organic light-emitting diode (TADF OLED) / 2,2′-(1,3-phenylene)-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole] (OXD-7) / bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS) / stability

References

[1] Tang C W, Vanslyke S A. Organic electroluminescent diodes. Applied Physics Letters, 1987, 51(12): 913–915

[2] Xie F M, An Z D, Xie M, Li Y Q, Zhang G H, Zou S J, Chen L, Chen J D, Cheng T, Tang J X. Tert-butyl substituted hetero-donor TADF compounds for efficient solution-processed non-doped blue OLEDs. Journal of Materials Chemistry C, Materials for Optical and Electronic Devices, 2020, 8(17): 5769–5776

[3] Kim H J, Godumala M, Kim S K, Yoon J, Kim C Y, Park H, Kwon J H, Cho M J, Choi D H. Color-tunable boron-based emitters exhibiting aggregation-induced emission and thermally activated delayed fluorescence for efficient solution-processable nondoped deep-blue to sky-blue OLEDs. Advanced Optical Materials, 2020, 8(14): 1902175

[4] Matsuo K, Yasuda T. Blue thermally activated delayed fluorescence emitters incorporating acridan analogues with heavy group 14 elements for high-efficiency doped and non-doped OLEDs. Chemical Science (Cambridge), 2019, 10(46): 10687–10697

[5] Yi C L, Ko C L, Yeh T C, Chen C Y, Chen Y S, Chen D G, Chou P T, Hung W Y, Wong K T. Harnessing a new co-host system and low concentration of new TADF emitters equipped with trifluoromethyl- and cyano-substituted benzene as core for high-efficiency blue OLEDs. ACS Applied Materials & Interfaces, 2020, 12(2): 2724–2732

[6] Wang Q, Tian Q S, Zhang Y L, Tang X, Liao L S. High-efficiency organic light-emitting diodes with exciplex hosts. Journal of Materials Chemistry C, Materials for Optical and Electronic Devices, 2019, 7(37): 11329–11360

[7] Zhang Q S, Li B, Huang S P, Nomura H, Tanaka H, Adachi C. Efficient blue organic light-emitting diodes employing thermally activated delayed fluorescence. Nature Photonics, 2014, 8(4): 326–332

[8] Zhang Q, Tsang D, Kuwabara H, Hatae Y, Li B, Takahashi T, Lee S Y, Yasuda T, Adachi C. Nearly 100% internal quantum efficiency in undoped electroluminescent devices employing pure organic emitters. Advanced Materials, 2015, 27(12): 2096–2100

[9] Duan C, Fan C, Wei Y, Han F, Huang W, Xu H. Optimizing the intralayer and interlayer compatibility for high-efficiency blue thermally activated delayed fluorescence diodes. Scientific Reports, 2016, 6(1): 19904

[10] Yang H, Liang Q Q, Han C M, Zhang J, Xu H. A posphanthrene oxide host with close sphere packing for ultralow-voltage-driven efficient blue thermally activated delayed fluorescence diodes. Advanced Materials, 2017, 29(38): 1700553

[11] Zhang Z, Ding D X, Wei Y, Zhang J, Han C M, Xu H. Excited-state engineering of universal ambipolar hosts for highly efficient blue phosphorescence and thermally activated delayed fluorescence organic light-emitting diodes. Chemical Engineering Journal, 2020, 382: 122485

[12] Gao F F, Du R M, Jiao F X, Lu G, Zhang J, Han C M, Xu H. A novel bridge-ring phosphine oxide host 5,10-[1,2]benzenophosphanthrene 5,10-dioxide for ultralow-voltage-driven blue thermally activated delayed fluorescence diodes. Advanced Optical Materials, 2020, 8(13): 2000052

[13] Zhang J, Ding D, Wei Y, Han F, Xu H, Huang W. Multiphosphine-oxide hosts for ultralow-voltage-driven true-blue thermally activated delayed fluorescence diodes with external quantum efficiency beyond 20%. Advanced Materials, 2016, 28(3): 479–485

[14] Cao X S, Chen Z X, Gong S L, Pan K, Zhou C J, Huang T, Chai D Y, Zhan Q, Li N Q, Zou Y, Liu H, Yang C L. Designing versatile sulfoximine as accepting unit to regulate the photophysical properties of TADF emitters towards high-performance OLEDs. Chemical Engineering Journal, 2020, 399: 125648

[15] Wu Z, Liu Y, Yu L, Zhao C, Yang D, Qiao X, Chen J, Yang C, Kleemann H, Leo K, Ma D. Strategic-tuning of radiative excitons for efficient and stable fluorescent white organic light-emitting diodes. Nature Communications, 2019, 10(1): 2380

[16] Zhao J, Wang Z J, Wang R, Chi Z G, Yu J S. Hybrid white organic light-emitting devices consisting of a non-doped thermally activated delayed fluorescent emitter and an ultrathin phosphorescent emitter. Journal of Luminescence, 2017, 184: 287–292

[17] Yang J, Zhao S L, Song D D, Xu Z, Qiao B, Wang P, Wei P. Highly efficient solution processed blue thermally activated delayed fluorescent organic light-emitting devices with a mixed hole injection layer. Spectroscopy and Spectral Analysis, 2020, 40(4): 1028–1033

[18] Yang J, Song D, Zhao S, Qiao B, Xu Z, Wang P, Wei P. Highly efficient and bright blue organic light-emitting devices based on solvent engineered, solution-processed thermally activated delayed fluorescent emission layer. Organic Electronics, 2019, 71: 1–6

[19] Kido J, Hongawa K, Okuyama K, Nagai K. Bright blue electroluminescence from poly(N-vinylcarbazole). Applied Physics Letters, 1993, 63(19): 2627–2629

[20] Hladka I, Lytvyn R, Volyniuk D, Gudeika D, Grazulevicius J V. W-shaped bipolar derivatives of carbazole and oxadiazole with high triplet energies for electroluminescent devices. Dyes and Pigments, 2018, 149: 812–821

[21] Zhang Z H, Jiang W, Ban X X, Yang M, Ye S H, Huang B, Sun Y M. Solution-processed efficient deep-blue fluorescent organic light-emitting diodes based on novel 9,10-diphenyl-anthracene derivatives. RSC Advances, 2015, 5(38): 29708–29717

[22] Jeltsch K F, Lupa G, Weitz R T. Materials depth distribution and degradation of a FIrpic based solution-processed blue OLED. Organic Electronics, 2015, 26: 365–370

[23] Jankus V, Abdullah K, Griffiths G C, Al-Attar H, Zheng Y H, Bryce M R, Monkman A P. The role of exciplex states in phosphorescent OLEDs with poly(vinylcarbazole) (PVK) host. Organic Electronics, 2015, 20: 97–102

[24] Girotto E, Pereira A, Arantes C, Cremona M, Bortoluzzi A J, Salla C A M, Bechtold I H, Gallardo H. Efficient terbium complex based on a novel pyrazolone derivative ligand used in solution-processed OLEDs. Journal of Luminescence, 2019, 208: 57–62

[25] Zhang Q, Zhang X W, Wei B. Highly efficient ultraviolet organic light-emitting diodes and interface study using impedance spectroscopy. Optik (Stuttgart), 2015, 126(18): 1595–1597

[26] Si C F, Chen G, Guo K P, Pan S H, Peng C Y, Wei B. Enhanced performance in inverted organic light-emitting diodes using Li ion doped ZnO cathode buffer layer. Molecular Crystals and Liquid Crystals (Philadelphia, Pa.), 2017, 651(1): 118–125

[27] Moon J, Cho H, Maeng M J, Choi K, Nguyen D T, Han J H, Shin J W, Kwon B H, Lee J, Cho S, Lee J I, Park Y, Lee J S, Cho N S. Mechanistic understanding of improved performance of graphene cathode inverted organic light-emitting diodes by photoemission and impedance spectroscopy. ACS Applied Materials & Interfaces, 2018, 10(31): 26456–26464

[28] Voitsekhovskii A V, Nesmelov S N, Dzyadukh S M, Kopylova T N, Degtyarenko K M. Impedance characterization of organic light-emitting structures with thermally activated delayed fluorescence. Physica Status Solidi A, Applications and Materials Science, 2020, 217(6): 1900847

[29] Gao M, Lee T, Burn P L, Mark A E, Pivrikas A, Shaw P E. Revealing the interplay between charge transport, luminescence efficiency, and morphology in organic light-emitting diode blends. Advanced Functional Materials, 2020, 30(9): 1907942

Acknowledgments

This work was financially supported by the National Key Research and Development Program of China (No. 2017YFB0404404), and the Open Fund of State Key Laboratory of Luminescent Materials and Devices (South China University of Technology), China.

RIGHTS & PERMISSIONS

2020 Higher Education Press