In this work, two host materials for blue TADF (thermally activated delayed fluorescence) OLEDs (organic light-emitting diodes) were designed and synthesized for improving the lifetime by ...incorporating pyridine core carbazole connected at different liking positions. These materials exhibit good thermal stability, high bond dissociation energy (BDE), and longer lifetime than the reference host. In particular, a blue TADF OLEDs system consisting of 4N-oCBP (9-(3-(2-(9H-carbazol-9-yl)phenyl)pyridin-4-yl)-9H-carbazole host and TCz-Trz (2,4,6-tris(2-(9H-carbazol-9-yl)phenyl)-1,3,5-triazine) dopant exhibited the best device performances with a maximum external quantum efficiency (EQE) of 16.2% and an improvement of 88% in operational lifetime (initial luminance of 200 cd/m2). This improved lifetime could be explained by the C–N BDE in the host molecular structure. The carbazole-based host molecule with different linking positions to the pyridine core developed in this study has considerable potential for improving the efficiency and lifetime of the TADF OLEDs device.
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•Two host materials for blue TADF OLEDs were designed and synthesized for improving the lifetime by incorporating pyridine core carbazole connected at different liking positions.•This improved lifetime could be explained by the C–N BDE in the host molecular structure.
Thin film humidity sensors were prepared using inorganic/organic hybrid polyelectrolytes, which were prepared from the sol–gel reaction of copolymers of 2-(methacryloyloxy)ethyldimethyl propyl ...ammonium bromide (MEDPAB),
n-butyl methacrylate (BMA) and 3-(trimethoxysilyl)propyl methacrylate (TMSPM) with colloidal silica. The humidity-sensitive polyelectrolytes were composed of copolymers with different contents of MEDPAB/BMA/TMSPM
=
60/30/10, 55/30/15 and 50/30/20. It was found that the resistance varied according to the content of MEDPAB and colloidal silica. The resistance ranged from 10
7 to 10
3
Ω between 20% and 95% RH, which was required for a humidity sensor operating at ambient humidity. The characteristics of humidity sensor, such as hysteresis, response time, temperature dependency, frequency dependency, water durability and long-term stability were further studied.
The challenges associated with thermally activated delayed fluorescence (TADF) materials are the reduced efficiency and lifetime because of the triplet-exciton lifetimes and thermal degradation of ...the devices owing to low molecular stabilities. To reduce the triplet-exciton lifetime, it is necessary to increase the rate of reverse intersystem crossing (RISC) and the intramolecular C–N bond dissociation energy (BDE) must be increased. In this study, a donor was introduced at the ortho position to reduce the energy gap between the singlet and triplet states and facilitate the expression of TADF properties. Three materials with increasing numbers of carbazole and CN− units and, consequently, increasing molecular stabilities: 4-(9H-carbazol-9-yl)-3-(4,6-diphenyl-1,3,5-triazin-2-yl)benzonitrile (Cz-mCNTrz), 3,3’-(6-phenyl-1,3,5-triazine-2,4-diyl)bis(4-(9H-carbazol-9-yl)benzonitrile) (DCz-mCNTrz), and 3,3′,3”-(1,3,5-triazine-2,4,6-triyl)tris(4-(9H-carbazol-9-yl)benzonitrile) (TCz-mCNTrz), were designed and synthesized. The best device performance of three materials, TCz-mCNTrz, exhibited 25.3% of maximum external quantum efficiency with highest photoluminescence quantum yield(PLQY) and smallest singlet-triplet energy gap. Moreover, lowest efficiency roll-off of 5.92%, as well as the longest lifetime at a 95-h at 5000 nits indicating increased anion BDE and rate of RISC after each addition of the carbazole and cyano moieties.
•Green TADF emitter were designed for increasing efficiency and lifetime of OLED device.•Three materials with increasing numbers of carbazole and CN− units were increased anion BDE and rate of RISC.•TCz-mCNTrz exhibited 25.3% of maximum external quantum efficiency with highest PLQY and smallest singlet-triplet energy gap.•TCz-mCNTrz exhibited lowest efficiency roll-off and longest lifetime at a 95-h at 5000 nits.
Recently, thermally activated delayed fluorescence (TADF) emitters have been successfully developed for highly efficient organic light-emitting diodes (OLEDs). In this study, we designed and ...synthesized three green TADF emitters with various positions of the CN group—3,3′,3''-(1,3,5-triazine-2,4,6-triyl)tris(2-(9H-carbazol-9-yl)benzonitrile) (TCz-2mCNTrz), 3,3′ ,3”-(1,3,5-triazine-2,4,6-triyl)tris(4-(9H-carbazol-9-yl)benzonitrile) (TCz-4mCNTrz), and 4,4′,4''-(1,3,5-triazine-2,4,6-triyl)tris(3-(9H-carbazol-9-yl)benzonitrile) (TCz-pCNTrz)—and evaluated their lifetime and efficiency by employing them in green TADF OLEDs. The synthesized materials exhibit different efficiencies and lifetimes owing to different bond dissociation energies (BDEs), which vary according to the position of the CN group. In particular, TCz-pCNTrz exhibits the maximum external quantum efficiency of 19.5% and the lowest efficiency roll-off, among the three materials. Further, TCz-pCNTrz exhibited a lifetime of 352 h in tests conducted under LT50@5000 nits. This resulted in a device with a higher lifespan than those of TCz-2mCNTrz (20.4 h) and TCz-4mCNTrz (50.0 h), in which CN groups were introduced at different positions. Thus, changes in the position of the CN group of TADF emitters can be expected to affect the device lifetime.
•Lifetime and efficiency of green TADF materials varies with CN-group positioning.•TCz-pCNTrz has least efficiency roll-off due to reducing TTA or TPA.•TCz-pCNTrz material with high anion BDE exhibits a lifetime of 352 h for tests conducted under LT50@5000 nits.
Humidity-sensitive epoxy monomer, glycidyl trimethyl ammonium chloride (GTMAC) was selected as the humidity-sensing resin. Polypropylene glycol diglycidyl ether (PPGDGE) and methyl tetrahydrophthalic ...anhydride (MTPHA) were used as a comonomer and a curing agent, respectively. The humidity-sensitive membranes were composed of GTMAC, PPGDGE and MTPHA. When impedance characteristics of the epoxy resins containing quaternary ammonium salts were measured, the impedance decreased linearly with an increase in the content of GTMAC in its semi-logarithmic graph. The impedance changed from 10
7 to 10
3
Ω between 30 and 90%RH, which was required for a common humidity sensor. Temperature dependence, frequency dependence and response time were also measured. The humidity-sensitive characteristics of the sensor did not change even after soaking in water.
Tetraphenylmethane and tetraphenylsilane were compared as building units for high‐triplet‐energy, charge‐transport materials. Tetraphenylsilane is effective as the building unit in electron‐transport ...materials, whereas tetraphenylmethane is suitable in hole‐transport materials (see figure; TSPO1=diphenylphosphine oxide‐4‐(triphenylsilyl), TSPA=phenyl‐N,N‐diphenyl‐4‐(triphenylsilyl)aniline, and TCPA=N,N‐diphenyl‐4‐tritylaniline).
The novel spirofluorene-7,9′-benzofluorene-based blue host material, 2-(10-phenylanthracene)-spirofluorene-7,9′-benzofluorene (BH-3P), was successfully prepared by reacting ...2-bromo-9,11-spirobenzofluorene-fluorene (
3) with 9-phenylanthracene-10-boronic acid through the Suzuki reaction. Diphenyl-4-(2-1,1;4,1terphenyl-4-yl-vinyl)-phenyl-amine (BD-1), 2-4′-(phenyl-4-vinylbenzeneamine)phenyl-spirofluorene-7,9′-benzofluorene (BH-3BD) and 4-2-naphthyl-4′ (phenyl-4-vinylbenzeneamine)phenyl (BD-1N) were used as dopant materials. Blue OLEDs with the configuration of ITO/DNTPD/α-NPD/BH-3P:5% dopant/Alq
3/Al–LiF were prepared from the BH-3P host and BD-1, BD-1N and BH-3BD dopants and they showed blue EL spectra at around 452
nm at 7
V and luminance efficiencies of 1.9–3.3
cd/A.
Carbazole modified terphenyl based high triplet energy host materials were developed for application as host materials for blue phosphorescent organic light-emitting diodes. Two terphenyl based ...materials, 9-(5″-phenyl-1,1′:2′,1″:3″,1′′′-quaterphenyl-3-yl)-9H-carbazole (CzTPPh) and 9-(3″,5″-di(pyridin-3-yl)-1,1:2′,1″-terphenyl-3-yl)-9H-carbazole (CzTPPy), were synthesized as the host materials with high triplet energies of 2.75 eV and 2.73 eV, respectively. The two host materials were evaluated as the host materials for blue phosphorescent organic light-emitting diodes and high quantum efficiencies of 20.2% and 15.7% were obtained in the CzTPPh and CzTPPy devices, respectively.
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•Carbazole modified terphenyl based high triplet energy host materials.•High quantum efficiency of 20.2% in blue phosphorescent organic light-emitting diodes.•High triplet energy over 2.70 eV for blue devices.
New spiro-type 5-biphenyl-spirofluorene-7,9′-benzofluorene (BH-1BP) and 5-diphenyl amine-spirofluorene-7,9′-benzofluorene (BH-1DPA) were synthesized for use as blue organic light-emitting host and ...dopant materials, respectively. Their optical properties, including their UV absorption, photoluminescence and energy levels, were measured and blue OLEDs were made from them. The structure of the blue device is ITO/DNTPD/α-NPD/BH-1BP:5% dopant/Alq
3 or ET4/Al–LiF. Here, α-NPD is used as the hole transport layer, DNTPD as the hole injection layer, BH-1DPA or diphenyl-4-(2-1,1;4,1terphenyl-4-yl-vinyl)-phenyl-amine (BD-1) as the blue dopant materials, Alq
3 or ET4 as the transporting layer and Al as the cathode. The blue devices doped with 5% BH-1DPA and BD-1 show blue EL emissions at 444–448
nm at 7
V. A high efficiency of 3.28
cd/A and the CIE coordinates (0.14, 0.11) at 7
V can be achieved from the devices composed of BH-1BP:5% BD-1/ET4.
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