Wet-process feasible novel carbazole-type molecular host for high efficiency phosphorescent organic light emitting diodes (original) (raw)
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2014 JMCC Wet process feasible carbazole host for OLEDs
2014
Wet-process organic light-emitting diodes (OLEDs) are crucial to realize cost-effective and large-area roll-to-roll fabrication of high quality displays and lightings. In this study, a wetprocess feasible carbazole based host material, 2-[4-(carbazol-9-yl)butyloxy]-9-[4-(carbazol-9-yl)butyl]carbazole (6), is synthesized, and two other carbazole hosts, 2-[5-(carbazol-9yl)pentyloxy]-9-[5-(carbazol-9-yl)pentyl]carbazole (7) and 2-[6-(carbazol-9-yl)hexyloxy]-9-[6-(carbazol-9-yl)hexyl]carbazole (8) are also synthesized for comparison. All three host materials exhibit high triplet energy, and possess high solubility in common organic solvents at room temperature. Doping a green phosphorescent emitter fac tris(2phenylpyridine)iridium (Ir(ppy) 3 ) into host 6 , the device shows an efficacy of 51 lmW -1 and current efficiency of 52 cdA -1 at 100 cdm -2 or 30 lmW -1 and 40.7 cdA -1 at 1,000 cdm -2 . The high efficiency may be attributed to the host possessing an effective host-to-guest energy transfer, the ability for excitons to generate on both host and guest, and excellent film integrity. Figure 3. Surface morphologies of the spin-coated films that comprise the pure hosts (a) 6, (b) 7, and (c) 8. All the films uniformities are improved upon increasing the glass transition temperature (T g ).
The Journal of Physical Chemistry C, 2018
Highly efficient deep-blue emission is crucial to realize energy efficient and high-quality display and solid-state lighting applications. A solution processable deep-blue emitter is essential for producing cost-effective large-area devices via roll-to-roll fabrication. Here, we demonstrate a highly efficient solution processable deep-blue organic light emitting diode by utilizing a carbazole-based fluorescent emitter 6-((9,9-dibutyl-7-((7-cyano-9-(2-ethylhexyl)-9H-carbazol-2yl)ethynyl)-9H-fluoren-2-yl)ethynyl)-9-(2-ethylhexyl)-9H-carbazole-2-carbonitrile (JV55). The resultant device showed a maximum external quantum efficiency (EQE) of 6.5% and an EQE of 5.5% at 100 cd m-2 with CIE coordinates of (0.16, 0.06). The optimized device showed a maximum EQE of 6.5%. Additionally, the deep-blue emission also realized a 101% color saturation according to the NTSC standard. The high efficiency may be attributed to engineering appropriate device architecture and enabling balanced carrier injection, effective host-to-guest energy transfer, the emissive layer having very high quantum yield of 91%, utilizing a host with high triplet energy so as to confine exciton on guest and low doping concentration inhibiting efficiency roll-off due to concentration quenching.
ACS applied materials & interfaces, 2017
An exciplex forming co-host system is employed to achieve highly efficient organic light-emitting diode (OLED) with good electroluminescent lifetime. The exciplex is formed at the interfacial contact of a conventional star-shaped carbazole hole-transporting material, 4,4',4"-tris(N-carbazolyl)-triphenylamine (TCTA) and a novel triazine electron-transporting material, 2,4,6-tris[3-(1H-pyrazol-1-yl)phenyl]-1,3,5-triazine (3P-T2T). The excellent combination of TCTA and 3P-T2T is applied as co-host of a common green phosphorescent emitter with almost zero energy loss. When Ir(ppy)2(acac) dispersed in such exciplex co-host system, OLED device with maximum external quantum efficiency of 29.6%, ultrahigh power efficiency of 147.3 lm/W, and current efficiency of 107 cd/A were successfully achieved. More importantly, the OLED device showed low efficiency roll-off and operational lifetime (τ80) of ~1020 minutes with the initial brightness of 2000 cd/m2, which is 56 times longer than ...
A wet- and dry-process feasible carbazole type host for highly efficient phosphorescent OLEDs
J. Mater. Chem. C, 2015
Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal's standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
Organic Electronics, 2006
Three new oxadiazole substituted carbazole derivatives 9-{4-[5-(4-tert-butylphenyl)-[1,3,4] oxadiazol-2-yl]-benzyl}-9 H-carbazole (t-CmOxa), 9-[4-5-phenyl-[1,3,4]oxadiazol-2-yl-benzyl]-9H-carbazole (p-CmOxa) and 9- [4-5-biphenyl-[1,3,4] oxadiazol-2-yl-benzyl]-9H-carbazole (d-CmOxa) were successfully synthesized and characterized by spectroscopy (NMR, UV-vis, mass spectrum and photoluminescence) and cyclic voltammetry measurements. Employing t-CmOxa as a host and Ir(DBQ) 2 (acac) (DBQ = dibenzo[f,h]quinoxaline, acac = acetylacetonate) as the dopant emitter, OLEDs with structures of ITO/NPB(30 nm)/Ir(DBQ) 2 (acac): t-CmOxa (30 nm, x%)/Alq 3 (30 nm)/Mg 0.9 :Ag 0.1 were fabricated without using BCP as the hole blocking layer. Red emission was obtained with CIE coordinates (x = 0.66, and y = 0.34) at 5 V and a very high external electroluminescent (EL) quantum efficiency of 9.5 ± 0.1%, and an energy conversion efficiency of 9.9 ± 0.1 lm/W were achieved for the device when the doping concentration x is equal to 4%.
Energy structure and electro-optical properties of organic layers with carbazole derivative
Thin Solid Films, 2014
Phosphorescent organic light emitting diodes are perspective in lighting technologies due to high efficient electroluminescence. Not only phosphorescent dyes but also host materials are important aspect to be considered in the devices where they are a problem for blue light emitting phosphorescent molecules. Carbazole derivative 3,6di(9-carbazolyl)-9-(2-ethylhexyl)carbazole (TCz1) is a good candidate and has shown excellent results in thermally evaporated films. This paper presents the studies of electrical properties and energy structure in thin films of spin-coated TCz1 and thermally evaporated tris[2-(2,4-difluorophenyl)pyridine]iridium(III) (Ir(Fppy) 3 ). The 0.46 eV difference of electron conduction level between TCz1 and Ir(Fppy) 3 compounds was obtained from the cyclic voltammetry and photoconductivity measurements. Temperature modulated space charge limited current (TM-SCLC) method is used to measure the local trapping states for charge carrier in the energy gap. The TM-SCLC measurements for the system TCz1 + 8 wt.% Ir(Fppy) 3 show a trapping state with the value of 0.4 eV which is comparable to the conduction level difference of these materials. It allows to conclude that Ir(Fppy) 3 molecules act as electron traps in the TCz1 matrix and the TM-SCLC method is applicable to investigate dopants as trapping states. To show the trap effect, an organic light emitting diode was made where the electroluminescent layer was a spin-coated host-guest system of TCz1 with incorporated 8 wt.% Ir(Fppy) 3 .
Advanced Functional Materials, 2016
The effi ciency roll-off in blue phosphorescent organic light emitting diodes (OLEDs) using different carbazole compounds as the host is systematically studied. While there is no signifi cant difference in device effi ciency, OLEDs using ter-carbazole as the host show a reduction in effi ciency roll-off at high luminance. Data from transient photoluminescence and electroluminescence measurements show that the lower triplet-triplet annihilation (TTA) and triplet-polaron quenching (TPQ) rates in devices with the ter-carbazole host compared with other carbazole hosts are the reasons for this reduced efficiency roll-off. It is also found that the host materials with low glass transition temperatures are more susceptible to the effi ciency roll-off problem.
Deep blue emission is crucial for achieving high-quality display and lighting, while high-efficiency is required to obtain energy-saving devices. A wet-and dry-process feasible efficient deep-blue emitter is highly desired to realize, respectively, low cost roll-to-roll fabrication of large area and high performance devices with precise deposition of organic layers. We demonstrate here high-efficiency and ultra-deep blue organic light-emitting diodes using a cyanofluorene-acetylene conjugate based emitter, 7,7 0 ((9,9dibutyl-9H-fluorene-2,7-diyl)bis(ethyne-2,1-diyl))bis(9,9-dipropyl-9H-fluorene-2 carbonitrile) (C3FLA-2).
Scientific Reports
The design of novel exciplex-forming co-host materials provides new opportunities to achieve high device performance of organic light emitting diodes (OLEDs), including high efficiency, low driving voltage and low efficiency roll-off. Here, we report a comprehensive study of exciplex-forming co-host system in OLEDs including the change of co-host materials, mixing composition of exciplex in the device to improve the performance. We investigate various exciplex systems using 5-(3-4,6-diphenyl-1,3,5-triazin-2-yl)phenyl-3,9-diphenyl-9H-carbazole, 5-(3-4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9-phenyl-9H-3,9′-bicarbazole, and 2-(3-(6,9-diphenyl-9H-carbazol-4-yl)phenyl)-4-phenylbenzo[4,5] thieno[3,2-d]pyrimidine, as electron transporting (ET: electron acceptor) hosts and 9,9′-dipenyl-9H, 9′H-3,3′-bicarbazole and 9-([1,1′-biphenyl]-4-yl)-9′-phenyl-9H,9′H-3,3′-bicarbazole as hole transporting (HT: electron donor) hosts. As a result, a very high current efficiency of 105.1 cd/A at 10 3 cd/m 2 and an extremely long device lifetime of 739 hrs (t 95 : time after 5% decrease of luminance) are achieved which is one of the best performance in OLEDs. Systematic approach, controlling mixing ratio of HT to ET host materials is suggested to select the component of two host system using energy band matching and charge balance optimization method. Furthermore, our analysis on exciton stability also reveal that lifetime of OLEDs have close relationship with two parameters; singlet energy level difference of HT and ET host and difference of singlet and triplet energy level in exciplex.