scholarly journals Effects of the Thickness of N,N'-diphenyl-N,N'-di(m-tolyl)-benzidine on the Electro-Optical Characteristics of Organic Light-Emitting Diodes

Materials ◽  
2019 ◽  
Vol 12 (6) ◽  
pp. 966
Author(s):  
Sang-Geon Park ◽  
Won Jae Lee ◽  
Min Jong Song ◽  
Johngeon Shin ◽  
Tae Wan Kim
Keyword(s):  
Current Efficiency ◽  
Current Density ◽  
Light Emitting Diodes ◽  
Light Emitting Diode ◽  
Hole Transport ◽  
Organic Light Emitting Diodes ◽  
Optical Characteristics ◽  
Driving Voltage ◽  
Light Emitting ◽  
Organic Light

We examined the electro-optical characteristics of organic light emitting diodes according to the N,N'-diphenyl-N,N'-di(m-tolyl)-benzidine (TPD) thicknesses. The thicknesses of TPD were varied from 5 nm to 50 nm. The current density of the device with a TPD thickness of 5 nm was 8.94 times higher than that with a thickness of 50 nm at a driving voltage of 10 V. According to the conduction–current characteristics of conductors, the current densities improved with a decreasing TPD thickness. Different from the current density–voltage characteristics, the current efficiency–current density characteristics showed an improved efficiency with a 50 nm TPD thickness. The current efficiencies of a device with a 5 nm TPD thickness at a driving voltage of 10 V was 0.148 and at a 50 nm TPD thickness 0.993 cd/A, which was 6.7 times higher than the 5 nm TPD thickness. These results indicated that hole transport in Organic Light-Emitting Diode (OLED) devices were more efficient with thin 5 nm TPD than with thick 50 nm TPD, while electron transport was more efficient with thick 50 nm TPD, which caused conflicting results in the current efficiency-current density and current density-voltage characteristics according to TPD thicknesses.

Substituted tetrapyrazolylporphyrins: application in organic light-emitting diodes

2005 ◽  
Vol 09 (12) ◽  
pp. 830-834 ◽  
Author(s):  
Can-Cheng Guo ◽  
Tie-Gang Ren ◽  
Jian-Xin Song ◽  
Qiang Liu ◽  
Kai Luo ◽  
...  
Keyword(s):  
Light Emitting Diodes ◽  
Hole Transport ◽  
Organic Light Emitting Diodes ◽  
Driving Voltage ◽  
Free Base ◽  
Red Emission ◽  
Light Emitting ◽  
Host Layer ◽  
Organic Light ◽  
Electron Donating Groups

Six substituted tetrapyrazolylporphyrins ( TAPyPH 2), meso-tetrakis(1-phenylpyrazol-4-yl)porphyrin ( TPPyPH 2), meso-tetrakis[1-(p-tolyl)pyrazol-4-yl] porphyrin ((p- CH 3) TPPyPH 2), meso-tetrakis[1-(p-methoxyphenyl)pyrazol-4-yl]porphyrin ((p- CH 3 O ) TPPyPH 2), meso-tetrakis[1-(p-chlorophenyl) pyrazol-4-yl]porphyrin ((p- Cl ) TPPyPH 2), meso-tetrakis[1-(p-bromophenyl)pyrazol-4-yl]porphyrin ((p- Br ) TPPyPH 2) and meso-tetrakis[1-(m-tolyl)pyrazol-4-yl]porphyrin ((m- CH 3) TPPyPH 2), were synthesized by the condensation of pyrrole with the corresponding substituted formylpyrazole and used as the doping materials in the Organic Light-Emitting Diodes (OLEDs) with hole-transport materials of N , N '-diphenyl- N , N '-bis (4-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine (TPD) within a tris(8-hydroxyquinoline) aluminum ( Alq 3) host layer. Both the electroluminescence properties of these OLEDs and effects of the peripheral substituents of the tetrapyrazolylporphyrins on EL properties of the OLEDs were studied. The tests found that the OLEDs using substituted tetrapyrazolylporphyrins ( TAPyPH 2) as the dopants had the saturated red emission at a concentration of 1.5 wt.%. The electron-donating groups of tetrapyrazolylporphyrins (for example, p- CH 3 and p- CH 3 O ) increased the luminance of OLEDs, while the electron-drawing groups (for example, p- Cl and p- Br ) decreased the luminance. The OLEDs using meso-tetrakis(1-phenylpyrazol-4-yl)porphyrin ( TPPyPH 2) as a dopant showed saturated red emission at 680 nm (CIE coordinates of x = 0.65, y = 0.31) with a luminance of 305 cd/m2 at a driving voltage of 25 V at concentration of 1.5 wt.%. Compared with OLEDs doped by the free-base tetraphenylporphyrin (TPPH2), the OLEDs doped by the tetrapyrazolylporphyrins had better luminance and higher emission efficiency. An explanation for these results was given based on the molecular structure and spectral properties of the porphyrin compounds.

Characterization of Hybrid Dual Emitting Layers in Blue Organic Light-Emitting Diodes by Controlling the Fluorescent Doping Concentration

2013 ◽  
Vol 1567 ◽  
Author(s):  
Bo Mi Lee ◽  
Nam Ho Kim ◽  
Ju-An Yoon ◽  
Woo Young Kim ◽  
Peter Mascher
Keyword(s):  
Current Density ◽  
Doping Concentration ◽  
Light Emitting Diodes ◽  
Dopant Concentration ◽  
Luminous Efficiency ◽  
Organic Light Emitting Diodes ◽  
Optical Characteristics ◽  
Light Emitting ◽  
Organic Light

ABSTRACTIn this study, we demonstrate blue organic light-emitting diodes (OLEDs) with a dual emitting layer (EML) configuration consisting of fluorescent and phosphorescent emitting materials. We investigated the influence of dopants on the electrical and optical characteristics of devices when controlling the fluorescent dopant concentration. The current density and luminance of device B doped with 12wt% BCzVBi was 141.6 mA/cm2 and 6582 cd/m2 at 10V, respectively. In addition, a maximum luminous efficiency of 8.11 cd/A, was achieved from device B. The corresponding Commission Internationale de l’E´ clairage (CIExy) coordinates of device D doped with 5wt% BCzVBi were (0.143, 0.255) at 6V.

Balancing Charge Injection and Transport in Organic Light-emitting Diodes with a Transparent Conductive Tungsten Oxide Layer

2014 ◽  
Vol 1629 ◽  
Author(s):  
R. Acharya ◽  
X. M. Li ◽  
Y. Lu ◽  
X. A. Cao
Keyword(s):  
Current Efficiency ◽  
Light Emitting Diodes ◽  
Charge Injection ◽  
Hole Transport ◽  
Organic Light Emitting Diodes ◽  
Transport Layer ◽  
Hole Injection ◽  
Hole Transport Layer ◽  
Light Emitting ◽  
Organic Light

ABSTRACTHigh-brightness green phosphorescent hybrid inorganic-organic light-emitting diodes (HyLEDs) and inverted HyLEDs (IHyLEDs) have been demonstrated. The devices comprised a transparent and conductive WO3 layer deposited by thermal evaporation, which improved both hole injection and transport, and led to more balanced charge injection and significant performance enhancement. At 20 mA/cm2, the HyLEDs had a low operation voltage of 6.1 V, 0.8 V lower than that of OLEDs with an organic hole transport layer. With an optimized layer structure, the HyLEDs reached 104 cd/m2 brightness at 7.3 V. At this brightness level, the current efficiency was 55.2 cd/A, 57% higher than that of the OLEDs. In the IHyLEDs, facile hole injection and transport through WO3 was balanced by electron injection from the indium-tin-oxide (ITO) cathode overcoated with nanometer-thick Ca, leading to a low turn-on voltage of ∼6 V. Brightness of 8133 cd/m2 was reached at 20 mA/cm2 and the corresponding current efficiency was 40 cd/A. The hybrid devices also exhibited markedly improved stability under constant-current stressing due to the robust WO3 hole transport layer.

Improve the Charge Balance of White Phosphorescent Organic Light Emitting Diodes Using Co-Doped Electron Transport Layer in Emitting Layer

2011 ◽  
Vol 287-290 ◽  
pp. 3051-3055
Author(s):  
Yu Sheng Tsai ◽  
Lin Ann Hong ◽  
Fuh Shyang Juang ◽  
Kuang Chih Lai ◽  
Chang Jun Lai ◽  
...  
Keyword(s):  
Electron Transport ◽  
Power Efficiency ◽  
Light Emitting Diodes ◽  
Hole Transport ◽  
Organic Light Emitting Diodes ◽  
Electron Transport Layer ◽  
Driving Voltage ◽  
Light Emitting ◽  
Organic Light ◽  
Luminance Efficiency

White phosphorescent organic light-emitting diodes (WPHOLED) with high efficiency and low driving voltage were achieved by incorporating an electron transport material (3TPYMB) into a hole transport-type host (TCTA) as a mixed-host structure. For electrons, the emitting layer is nearly barrier-free until they reach the region of exciton formation, which keeps the driving voltage low. Therefore, improved the charge carrier balance within the emitting layer and enhanced the power efficiency of device. White PHOLED at a luminance of 1000 cd/m2 shown a driving voltage of 4.38 V, luminance efficiency of 36.1 cd/A, and power efficiency of 26.4 lm/W was observed. Furthermore, the power efficiency can be improved to 34.27 lm/W, and luminance efficiency to 46.7 cd/A by attaching a brightness enhancement film (BEF).

Use of Versatile Binaphthalene Derivative in Chromatic-Stability Non-Doped White Organic Light Emitting Diodes

2012 ◽  
Vol 490-495 ◽  
pp. 3887-3891
Author(s):  
Fei Fei Wang ◽  
Yan Fang Lv ◽  
Peng Chao Zhou ◽  
Hong Lin ◽  
Na Wei ◽  
...  
Keyword(s):  
Thin Layer ◽  
Current Efficiency ◽  
Current Density ◽  
Light Emitting Diodes ◽  
Organic Light Emitting Diodes ◽  
Light Emitting ◽  
Organic Light ◽  
Color Rendering Index ◽  
Low Efficiency ◽  
Color Rendering

We have investigated the properties of the ultra-thin layer all-fluorescent nondoped white organic light emitting diodes based on blue-emitting binaphthalene derivative (BN) and ultra-thin green and red emitters. By optimizing the thickness of BN, we found that the device exhibited a high color rendering index (CRI) of 84 and high chromatic-stability with the Commission International de L’Eclairage coordinates shifting from (0.26, 0.32) to (0.27, 0.33) as the luminance increased from 40 to 10645 cd/m2. In addition, we also achieved a low current efficiency roll-off, which current efficiency only reduced from 3.77 cd/A to 3.36 cd/A when the current density increased from 13 mA/cm2 to 104 mA/cm2. High CRI and low efficiency roll-off are of significance for the applications of organic light-emitting diodes in display and lighting.

scholarly journals Unravelling the electron injection/transport mechanism in organic light-emitting diodes

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Tsubasa Sasaki ◽  
Munehiro Hasegawa ◽  
Kaito Inagaki ◽  
Hirokazu Ito ◽  
Kazuma Suzuki ◽  
...  
Keyword(s):  
Work Function ◽  
Transport Mechanism ◽  
Light Emitting Diodes ◽  
Light Emitting Diode ◽  
Electron Injection ◽  
Organic Light Emitting Diodes ◽  
Light Emitting ◽  
Organic Light Emitting Diode ◽  
Organic Light ◽  
Materials Used

AbstractAlthough significant progress has been made in the development of light-emitting materials for organic light-emitting diodes along with the elucidation of emission mechanisms, the electron injection/transport mechanism remains unclear, and the materials used for electron injection/transport have been basically unchanged for more than 20 years. Here, we unravelled the electron injection/transport mechanism by tuning the work function near the cathode to about 2.0 eV using a superbase. This extremely low-work function cathode allows direct electron injection into various materials, and it was found that organic materials can transport electrons independently of their molecular structure. On the basis of these findings, we have realised a simply structured blue organic light-emitting diode with an operational lifetime of more than 1,000,000 hours. Unravelling the electron injection/transport mechanism, as reported in this paper, not only greatly increases the choice of materials to be used for devices, but also allows simple device structures.

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