Oligomers containing pyridinyl-substituted carbazole rings as host materials for phosphorescent OLEDs (original) (raw)
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Molecules, 2021
Pyridinyl-carbazole fragments containing low molar mass compounds as host derivatives H1 and H2 were synthesized, investigated, and used for the preparation of electro-phosphorescent organic light-emitting devices (PhOLEDs). The materials demonstrated high stability against thermal decomposition with the decomposition temperatures of 361–386 °C and were suitable for the preparation of thin amorphous and homogeneous layers with very high values of glass transition temperatures of 127–139 °C. It was determined that triplet energy values of the derivatives are, correspondingly, 2.82 eV for the derivative H1 and 2.81 eV for the host H2. The new derivatives were tested as hosts of emitting layers in blue, as well as in green phosphorescent OLEDs. The blue device with 15 wt.% of the iridium(III)[bis(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate (FIrpic) emitter doping ratio in host material H2 exhibited the best overall characteristics with a power efficiency of 24.9 lm/W, a current eff...
Efficient red phosphorescent OLEDs employing carbazole-based materials as the emitting host
Dyes and Pigments, 2015
We report on the synthesis and characterization of a new series of electro-active carbazole-based compounds. The derivatives are thermally stable amorphous materials with glass transition temperatures in the range of 54e93 C. Electron photoemission spectra of thin layers of the materials show ionization potential in the range of 5.4e5.5 eV. The carbazole-based derivatives are fully characterized and their spectroscopic properties are determined by absorption and photoluminescence. All developed materials and commonly-used tris(4-carbazoyl-9-ylphenyl)amine (TCTA) were used as hosts in red phosphorescent organic light-emitting diodes (OLEDs) for comparison. Results indicate that a device with 3-[bis(9-ethylcarbazol-3-yl)methyl]-9-hexylcarbazole exhibited superior performance with peak efficiencies of 8.4%, 5.3 cd/A and 5.5 lm/W.
Organic Light Emitting Materials and Devices XIII, 2009
The properties of phosphorescent fac tris(2-phenylpyridine) iridium [Ir(ppy 3 )]-doped poly(N-vinyl carbazole) (PVK)/4,7-diphenyl-1,10-phenanthroline (Bphen) polymer/small molecular hybrid OLEDs are described. For optimal BPhen thickness, the power efficiency of the devices exceeds 30 lm/W. The low-temperature electroluminescence-detected magnetic resonance (ELDMR) exhibits the well-known negative spin 1/2 resonance attributed to enhanced formation of trions, but the positive spin 1/2 resonance, typically observed at low temperature or at high current density, is not observed. The OLEDs' performance and the ELDMR results are discussed in relation to the nature of the defects and their density in these devices.
New carbazole-indan-1,3-dione- based host materials for phosphorescent organic light emitting diodes
Molecular Crystals and Liquid Crystals, 2016
New carbazole-and indan-1,3-dione-based low molecular weight derivatives were synthesized and characterized by mass spectrometry and 1 H NMR spectroscopy. Thermal behaviour of the derivatives was demonstrated by thermo-gravimetric analysis and differential scanning calorimetry. The materials were found to show very high thermal stability having initial thermal degradation temperatures in the range of 398-401°C. Glass transition temperatures of the amorphous molecular materials were in the rage of 80-114°C. The derivatives were tested as host materials in blue phosphorescent organic light emitting diodes with iridium(III)[bis(4,6-difluorophenyl)pyridinato-N,C2 ]picolinate as the guests. One of the blue OLED devices demonstrated rather low turn-on voltage of 5.0 V, a maximum luminance efficiency of 2.73 cd/A and maximum brightness of about 220 cd/m 2 .
Dyes and Pigments, 2011
Yellow iridium complexes Ir(PPOHC) 3 and (PPOHC) 2 Ir(acac) (PPOHC: 3-(5-(4-(pyridin-2-yl)phenyl)-1,3,4-oxadiazol-2-yl)-9-hexyl-9H-carbazole) were synthesized and characterized. The Ir(PPOHC) 3 complex has good thermal stability with 5% weight-reduction occurring at 370 C and a glass-transition temperature of 201 C. A polymeric light-emitting diode using the Ir(PPOHC) 3 complex as a phosphorescent dopant showed a luminance efficiency of 16.4 cd/A and the maximum external quantum efficiency of 6.6% with CIE coordinates of (0.50, 0.49). A white polymeric light-emitting diode was fabricated using Ir(PPOHC) 3 which showed a luminance efficiency of 15.3 cd/A, with CIE coordinates of (0.39, 0.44). These results indicate that the iridium complexes containing a linked carbazoleeoxadiazole unit are promising candidates in highefficiency electroluminescent devices.
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%.
A series of novel carbazole-based materials, DPACz1, DPACz2 and DPACz3 having diphenylamino moieties at 1-and 8-positions of carbazole have been synthesized and characterized for the first time. The introduction of diphenylamino substituents at 1-or 1,8-positions of carbazole resulted into increase of the band-gap compared with the previously reported 3,6-or 2,7-substituted ones. The HOMO levels increased from DPACz1 to DPACz2 with the addition of one additional diphenylamino unit, and further increased in case of DPACz3, a dimer of DPACz1 having a benzidine moiety. The materials have high triplet energy levels of 2.68, 2.60 and 2.45 eV, respectively. Based on suitable HOMO levels and high triplet energies, the newly synthesized diphenylaminocabazoles were investigated for their potential as solution-processable host materials for green phosphorescent OLEDs with the device configuration, [ITO/ PEDOT:PSS/Emitting layer/TPBi/CsF/Al]. All the devices emitted typical green light with high luminance and had low turn-on voltages along with good luminous efficiencies which were further improved by adjusting charge balance using PBD, as a co-host. The basic characteristics and the preliminary OLED results showed the usefulness of our new materials, and this kind of 1-/1,8-substitution of carbazole would open a new way of materials design.
Solution-processed blue phosphorescent OLEDs with carbazole-based polymeric host materials
Organic Electronics, 2015
A new carbazole-based polymer PEPEK varying from the previously reported PEPK by the length of the spacer between the polymer backbone and the pendent carbazole moiety was investigated as polymeric host for solution-processed devices. Interestingly, if the two polymers are structurally close since the length of the alkyl chain only differs from one carbon atom, the previously reported PEPK gave higher performances than the newly synthesized PEPEK when tested as host for the wide bandgap triplet emitter FIrpic. To optimize electroluminescence performances, two device configurations were examined. On doping the emissive layer of phosphorescent organic light-emitting devices (OLEDs) at 16 wt% with FIrpic, best PEPK-based OLEDs gave an efficacy of 15.14 cd/A whereas PEPEK-based devices furnished an efficiency of 12.17 cd/A in the same conditions. To determine the origin of this unexpected behavior, the new polymer PEPEK was characterized by UV-visible absorption and luminescence spectroscopy as well as cyclic voltammetry. Thermal properties of PEPEK were also examined and compared to those of PEPK.
The role of carbazole in organic light-emitting devices
Synthetic Metals, 1996
New organic oligomers and polymers based on the carbazole molecule are explored for possible applications in light-emitting devices. In one case, (butyl-or octyl-) carbazole dimers and poly(N-butyl-3,6-carbazolylene) polymer were used as the hole-transporting and lightemitting layer in multilayer light-emitting diodes (LEDs). These devices yielded bright blue light (as much as about 6000 cd m-2) with high external quantum (about 10%) and luminance efficiencies (about 21m W-1). The other case involved ([3-octylthiophene J-[bis-(Nethyl or octyl carbazolylene) ]) multiblock copolymers as the active emitting layer in single-layer LEDs. Color tuning was achieved in these devices by changing the number of monomer units contained in the thiophene chain. We also observed an increase of the external quantum efficiency in diodes based on the copolymers with short thiophene segments that we attributed to a more balanced charge injection.