• Transactions on Electrical and Electronic Materials
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• v.6 no.5
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• pp.221-224
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• 2005

To overcome of poor electron injection in organic light-emitting diodes (OLEDs) with Al cathode, a thin layer of inorganic insulating materials, like as LiF, is inserted between an Al cathode and an organic electron transport layer. Though the device, mentioned above, improves both turn on voltage and luminescent properties, it has some problems like as thickness restriction, less than 2 nm, and difficulty of deposition control. On the other hand, Li organic complex, Liq, is less thickness restrictive and easy to deposit and it also enhances the performance of devices. This paper reports the improved electron injection on OLEDs with another I A group metal complex, Potassium quinolate (Kq), as an electron injection material. OLEDs with organic complexes showed improved turn-on voltage and luminous efficiency which are remarkably improved compared to OLEDs with Al cathode. Especially, OLEDs with Kq have longer life time than OLEDs with Liq.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.90-90
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• 2012

The electron/hole injections in organic electronic devices have long been an issue due to the large energy level mismatches between electrode and organic layer. To utilize the organic materials in electronic devices, functional thin layers have been used, which reduce the electron/hole injection barrier from electrode to organic material. Typically, inorganic compounds and organic molecules are used as an electron and hole injection layer, respectively. Recently, CsN3 and 1,4,5,8,- naphthalene-tetracarboxylic-dianhydride (NTCDA) are reported as a potential electron and hole injection layers. CsN3 shows unique properties that it breaks into Cs and N and thus Cs can dope organic layer into n-type. On the other side, hole injection anode, NTCDA forms gap states with anode material. In this presentation, we show the electronic structure changes upon the insertion of CsN3 and NTCDA at proper interfaces to reduce the charge injection barriers. These barrier reductions are correlated with device characteristics.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.555-558
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• 2004

The efficiency of electron injection from the cathode is strongly dependent on the thickness of the LiF buffer-layer. We used LiF to electron Injection layer. We compared characteristics of organic light emitting device changing LiF thin film thickness from 1.0 m to 10.0 nm. Experiment result, we found that LiF thickness has the optimized electrical characteristics in 3.0 m. In this paper, we did research about electrical characteristics of organic light emitting device by LiF thickness change using method numerical analysis method. We proved adequate experimental results that compare results of numerical analysis, and come out through an experiment results is validity.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.439-440
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• 2007

To enhance the electron injection from the cathode of organic light-emitting diodes (OLEDs), We have studied characteristics of device that electron injection layer(EIL) is inserted between emissive layer and cathode. We fabricated bi-layer cathode $Li_2O$(x nm)/Al(100nm) and LiF(x nm)/Al(100nm) using LiF and $Li_2O$ as an electron injection layer. We analyzed the current efficiency, luminance efficiency, and external quantum efficiency of the device by varying the thickness of $Li_2O$ and LiF to be 0.5nm, 1nm, or 3nm. Using the EIL, we have obtained the efficiency of 7cd/A and the luminance of $20,000cd/m^2$. There is an improvement of efficiency by more than 3 times than the device without the $Li_2O$ layer.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.69-70
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• 2006

We studied increasement of efficiency of Organic Light-emitting Diodes depending on thickness variation of LiF, Material of Electron Injection Layer in structure of ITO/Hole Injection Layer (PTFE)/Hole Transportion Later (TPD)/Emitting Layer (Alq3)/Electron Injection Layer (LiF)/Al. TPD and $Alq_3$ is deposited as rate of 1.3~1.5 [${\AA}/s$] in high vacuum ($5{\times}10^{-6}$ [torr]). In result of these studies, we can know maximum efficiency in 0.7 [nm], thickness of LiF. And samples with electron injection material are increased about 5-fold in maximum efficiency in compare with sample without electron injection material.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.475-476
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• 2005

Efficient electron injection is essential to achieve bright and efficient organic light-emitting diodes (OLEDs). In spite of high work function of Al, it is a common cathode because of its stability. In this paper, to overcome the poor electron injection in OLEDs with Al cathode, OLEDs with various composite cathodes were fabricated and investigated using a conventional OLEDs structure of indium tin oxide ITO/NPB(40 nm)/$Alq_3$(50 nm)/Al. composite cathodes were composed of alkaline materials such as Ca and Li, Al deposition or codeposited with AI. We showed best performance at the device with composite cathode (LiF/Al).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.8
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• pp.678-681
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• 2011

We have investigated the effect of organic thin film on the driving voltage of OLED (organic light emitting diode) by inserting a 5 nm thick 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) or triphenylphosphineoxide ($Ph_3PO$) between tris-(8-hydroxyquinoline)aluminum ($Alq_3$) electron transport layer and 4,4'-bis(2,2'-diphyenylvinyl)-1,1'-biphenyl (DPVBi) emission layer. The device with 5 nm thick $Ph_3PO$ layer exhibited higher maximum current efficiency and lower driving voltage than the device with BCP layer, resulting from better electron injection from $Alq_3$ to DPVBi in the device with $Ph_3PO$ layer.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1015-1018
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• 2004

We investigate the influence of the New Electron Injection Layers (EIL) on the performance of the Alkali Metal Complex vapor-deposited Organic Light Emitting Diodes(OLED). Two different Alkali Metal Complex were used; Lithium Quinolate (Liq), and Sodium Quinolate (Naq). In all cases, $Alq_3$ was the Electron Transporting Layer (ETL). We measure and compare the current density-voltage (J-V) and luminance-voltage (L-V) characteristics. We concluded that the turn-on voltage, and luminance efficiency are controlled by the type of EIL material used. We show the longer life-time OLED with Alkali Metal Complex EIL than OLED with LiF EIL. And we show the Optimized Alkali Metal Complex thickness is 3nm. Existent LiF to because is inorganic material, there is trouble to do epitaxy into thin layers but regulates the thickness in case of Alkali Metal Complex matter characteristic that is easy be. Alkali Metal Complex also appeared by sensitive thing in thickness than LiF If utilize this material, It is thought much advantages may be at common use of OLED.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1805-1808
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• 2006

In this paper, we describe a versatile use of fullerene(C60) as a charge transporting material for organic light-emitting diodes. The use of fullerene as a buffer layer for an anode, a doping material for hole transport layer, and an electron transport layer was investigated. Fullerene improved the hole injection from an anode to a hole transport layer by lowering the interfacial energy barrier and enhanced the lifetime of the device as a doping material for a hole transport layer. In addition, it was also effective as an electron transporting material to get low driving voltage in the device.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.10
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• pp.897-902
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• 1998

We prepared Organic LED with a two layer structure by vacuum evaporation. The diode consisted of hole transfer layer (thickness of 30, 50, 70 nm) and electron transfer layer (thickness of 70, 50, 30 nm) material, which was N, N'-diphenyl- N, N'-bis-(3-methyl phenyl)-1,1'-diphenyl-4,4'-diamine)(TPD) and tris(8-hydroxy quinoline) aluminum(Alq3), respectively. We investigated EL properties of the LED with various thickness and cathode electrode. The best results were obtained when thickness of the electron layer is equal to that of emission layer and when AlLi alloy was used as a cathode. The EL intensity, luminance and efficiency of organic LED with equal of layer thick were improved seven, three and two times, respectively. Alq3 was ionized by carrier injection from cathode and could produce exitons. After electron-hole pairs were formed by combination of the electrons and holes at the emission layer, Alq3 layer emitted light.