• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.147-147
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• 2015

The multilayer structure of the organic light emitting diode has merits of improving interfacial characteristics and helping carriers inject into emission layer and transport easier. There are many reports to control hole injection from anode electrode by using transition metal oxide as an anode buffer layer, such as V2O5, MoO3, NiO, and Fe3O4. In this study, we apply thin films of LiF which is usually inserted as a thin buffer layer between electron transport layer(ETL) and cathode, as an anode buffer layer to reduce the hole injection barrier height from ITO. The thickness of LiF as an anode buffer layer is tested from 0 nm to 1.0 nm. As shown in the figure 1 and 2, the luminous efficiency versus current density is improved by LiF anode buffer layer, and the threshold voltage is reduced when LiF buffer layer is increased up to 0.6 nm then the device does not work when LiF thickness is close to 1.0 nm As a result, we can confirm that the thin layer of LiF, about 0.6 nm, as an anode buffer reduces the hole injection barrier height from ITO, and this results the improved luminous efficiency. This study shows that LiF can be used as an anode buffer layer for improved hole injection as well as cathode buffer layer.

• 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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• 2005.11a
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• pp.277-278
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• 2005

Admittance Spectroscopic analysis was applied to study the effect of LiF buffer layer and to model the equivalent circuit for poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV)-based polymer light emitting diodes (PLEDs) with the LiF cathode buffer layer. The single layer device with ITO/MEH-PPV/Al structure can be modeled as a simple parallel combination of resistor and capacitor. Insertion of a LiF layer at the Al/MEH-PPV interface shifts the highest occupied molecular orbital level and the vacuum level of the MEH-PPV layer as a result the barrier height for electron injection at the Al/MEH-PPV interface is reduced. The admittance spectroscopy measurement of the devices with the LiF cathode buffer layer shows reduction in contact resistance ($R_c$), parallel resistance ($R_p$) and increment in parallel capacitance ($C_p$).

• Journal of the Semiconductor & Display Technology
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• v.10 no.1
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• pp.27-32
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• 2011

In this study, we have investigated the power conversion efficiency of organic solar cells utilizing conjugated polymer/fullerene bulk-hetero junction(BHJ) device structures. We have fabricated poly(3-hexylthiophene)(P3HT), poly[2methoxy-5-(3',7'-dimethyloctyl-oxy)-1-4-phenylenevinylene] as an electron donor, [6,6]-phenyl $C_{61}$ butyric acid methylester(PCBM-$C_{61}$)as an electron acceptor, and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS) used as a hole injection layer(HIL), after fabricated active layer, between active layer and metal cathode(Al) deposited LiF interlayer(5 nm). The properties of fabricated organic solar cell(OSC) devices have been analyzed as a function of different thickness. The electrical characteristics of the fabricated devices were investigated by means J-V, fill factor(FF) and power conversion efficiency(PCE). We observed the highest PCEs of 0.628%(MDMO-PPV:PCBM-$C_{61}$) and 2.3%(P3HT:PCBM-$C_{61}$) with LiF inter-layer at the highest thick active layer, which is 1.3times better than the device without LiF inter-layer.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1056-1058
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• 2005

Electrical and optical characteristics of MEH-PPV-based PLEDs with the LiF anode interfacial layer were investigated. The maximum luminance efficiency of the device with a LiF anode interfacial layer of 1-nm-thick was 3.0 lm/W, which is higher than 1.97 lm/W of the device without a LiF layer. By inserting LiF, excess injected holes from ITO anode can be blocked and hence the recombination ratio of electrons and holes can be increased in the emitting layer to improve device efficiency.

• Transactions on Electrical and Electronic Materials
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• v.18 no.2
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• pp.89-92
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• 2017

The performance of three-layered organic light-emitting diodes (OLEDs) was investigated using TPD hole-transport and injection layers, Teflon-AF, and the electron-injection layer of $Li_2CO_3$ and LiF. The OLEDs were manufactured in a structure of TPD/$Alq_3$/LiF, TPD/$Alq_3$/$Li_2CO_3$, and AF/$Alq_3$/LiF using low-molecular organic materials. In three different three-layered OLEDs, it was found that the device with the TPD/$Alq_3$/LiF structure shows higher performance in maximum luminance, and maximum external quantum efficiency compared to those of the device with TPD/$Alq_3$/$Li_2CO_3$ and TPD/$Alq_3$/LiF by 35% and 17%, and 193% and 133%, respectively. It is thought that the combined LiF/Al cathode contributes to a reduced work function and improves an electrical conduction mechanism due to the electron injection rather than the hole transport, which then increases a recombination rate of charge carriers.

• 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.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.9
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• pp.696-700
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• 2010

We fabricated red and blue organic light emitting display (OLEDs) which had the two kinds of multi-structure of ITO/HIL/HTL/EML/ETL/LiF/Al and ITO/HIL/HTL/EML/ETL/LiF/Al/LiF. In the case of red OLED that had LiF/Al/LiF structure compared to LiF/Al structure, the current density increased from 4.3 mA/$cm^2$ to 7.3 mA/$cm^2$, and the brightness increased from 488 cd/$m^2$ to 1,023 cd/$m^2$ at 7.0 V, and as a result the current efficiency was improved from 11.28 cd/A to 13.95 cd/A. Also in the case of blue OLED that had LiF on Al cathode layer, the current density increased from 1.2 mA/$cm^2$ to 1.8 mA/$cm^2$, and the brightness increased from 45 cd/$m^2$ to 85 cd/$m^2$ at 7.0 V, and as a result the current efficiency was improved from 3.69 cd/A to 4.82 cd/A. Through these experimental results it could be suggested that the LiF layer formed on Al prevents the oxidation of Al surface, and the electrode resistance become low with increase of supplied electrons, therefore the brightness and the efficiency are improved from the influence to the well-balanced bonding of electron and hole at emitting layer.

• Journal of Surface Science and Engineering
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• v.42 no.6
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• pp.287-293
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• 2009

The passivation films with epoxy layer on LiF, $SiN_x$ and LiF/$SiN_x$ inorganic layer were fabricated on OLED to protect device from the direct damage of $O_2$ and $H_2O$ and to apply for a buffer layer between OLED device and passivation multi-layer with organic/inorganic hybrid structure as to diminish the thermal stress and expansion. Red OLED doped with 1 vol.% Rubrene in $Alq_3$ was used as a basic device. The device structure was multi-layer of ITO(150 nm) / ELM200_HIL(50 nm) / ELM002_HTL(30 nm) / $Alq_3$: 1 vol.% Rubrene(30 nm) / $Alq_3$(30 nm) / LiF(0.7 nm) / Al(100 nm). LiF/epoxy applied as a protective layer didn't contribute to the improvement of life time. While in case of $SiN_x$/epoxy, damage was done in the passivation process because of difference in heat expansion between films which could occur during the formation of epoxy film. Using LiF/$SiN_x$/epoxy improved lifetime significantly without suffering damage in the process of forming films, therefore, the best structure of passivation film with inorganic/epoxy layers was LiF/$SiN_x$/E1.

• Journal of the Semiconductor & Display Technology
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• v.21 no.1
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• pp.71-74
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• 2022

For the process simplification in the fabrication of organic light emitting diode(OLED), top emission OLED (TEOLED) was fabricated without lithium fluoride(LiF) used as an electron injection layer (EIL). After co-deposition of Mg and Ag with a different process conditions, a cathode material adjacent to EIL was optimized when Mg and Ag have a ratio of 1:9 considering sheet resistance and transmittance. From the energy band diagram of TEOLED, band gap difference between Trisaluminium (Alq3) and Mg:Ag cathode show the difference of 0.4 eV according to the usage of LiF The fabricated TEOLED without LiF showed the improvement of 5.2 % and 2.7 % in the luminance and the current density comparing that with LiF. The results show there is no significant difference in OLED characteristics regardless of LIF layer in the TEOLED structures.