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Frontiers of Optoelectronics

ISSN 2095-2759

ISSN 2095-2767(Online)

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Front. Optoelectron.    2021, Vol. 14 Issue (4) : 491-498    https://doi.org/10.1007/s12200-020-1069-0
RESEARCH ARTICLE
Improved stability of blue TADF organic electroluminescent diodes via OXD-7 based mixed host
Weiguang LI1,2, Jie TANG1,2, Yanqiong ZHENG1(), Junbiao PENG3, Jianhua ZHANG1, Bin WEI1(), Xifeng LI1
1. Key Laboratory of Advanced Display and System Applications of Ministry of Education, School of Mechatronic Engineering and Automation, Shanghai University, Shanghai 200072, China
2. School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China
3. State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China
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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.
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     
Corresponding Author(s): Yanqiong ZHENG,Bin WEI   
Just Accepted Date: 05 November 2020   Online First Date: 27 November 2020    Issue Date: 06 December 2021
 Cite this article:   
Weiguang LI,Jie TANG,Yanqiong ZHENG, et al. Improved stability of blue TADF organic electroluminescent diodes via OXD-7 based mixed host[J]. Front. Optoelectron., 2021, 14(4): 491-498.
 URL:  
https://academic.hep.com.cn/foe/EN/10.1007/s12200-020-1069-0
https://academic.hep.com.cn/foe/EN/Y2021/V14/I4/491
Fig.1  (a) Molecular structures of PEDOT:PSS, DMAC-DPS, PVK, Bphen, OXD-7, and DPEPO. (b) Energy-level diagram of the co-host device. PL spectra of the pristine 40 nm DMAC-DPS film (c) and EML blend films (40 nm) with single host and co-host via annealing at 80°C and 100°C, respectively (d) on quartz substrates
Fig.2  AFM surface topographic and 3D images for different EML blend films on ITO substrates. (a) PVK:OXD-7:DMAC-DPS EML annealed at 80°C for 30 min. (b) PVK:OXD-7:DMAC-DPS EML annealed at 100°C. (c) PVK:DMAC-DPS EML annealed at 80°C. (d) PVK:DMAC-DPS EML annealed at 100°C
Fig.3  EL characteristics of the TADF devices with PVK:DMAC-DPS or PVK:OXD-7:DMAC-DPS EML by spin-coating at 3000 r/min for 30 s or 60 s and annealing at 80°C for 30 min. (a) Current density-voltage-luminance (J-V-L). (b) Current efficiency (CE)-luminance. (c) Power efficiency (PE)-luminance, inset of (c) is the corresponding EL spectra. (d) EQE-current density, inset of (d) is the normalized EQE spectra
host time/s Lmax/(cd·m−2) CEmax/(cd·cm−2) PEmax/(lm·W−1) EQEmax/%
PVK 30 228 2.08 1.18 1.37
PVK 60 217 1.63 0.85 1.12
PVK:OXD-7 (6:3, wt%) 30 207 0.59 0.41 0.51
PVK:OXD-7 (6:3, wt%) 60 238 0.46 0.29 0.40
Tab.1  EL characteristics of ITO/PEDOT:PSS (30 nm)/host:DMAC-DPS (15 nm)/DPEPO (10 nm)/Bphen (30 nm)/LiF (0.8 nm)/Al (80 nm) with various EMLs by spin-coating at 3000 r/min for 30 s or 60 s via annealing at 80°C for 30 min
Fig.4  EL characteristics of TADF devices with PVK:OXD-7:DMAC-DPS EML via spin-coating at 2000 r/min for 30 s. (a) Current density-voltage-luminance (J-V-L). (b) Current efficiency (CE)-luminance. (c) Power efficiency (PE)-luminance. (d) EQE-current density, inset of (d) is the corresponding EL spectra
T/°C Lmax/(cd·m−2) Vturn-ona/V CEmax/(cd·cm−2) PEmax/(lm·W−1) EQEmax/%
80 36.5 7.5 3.15 1.17 1.41
100 243 5.8 2.32 0.82 1.31
Tab.2  EL characteristics of ITO/PEDOT:PSS (30 nm)/PVK:OXD-7:DMAC-DPS (6:3:1, wt%, 20 nm)/DPEPO (10 nm)/Bphen (30 nm)/LiF (0.8 nm)/Al (80 nm) at various annealing temperatures (T) for the EML by spin-coating at 2000 r/min for 30 s
Fig.5  Impedance spectroscopy characteristics (Z-f and φ-f) for the TADF OLEDs with hosts of PVK:OXD-7, PVK, and OXD-7, respectively
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