• 한국정보디스플레이학회:학술대회논문집
• /
• 2002.08a
• /
• pp.105-107
• /
• 2002

The device characteristics and the interface electronic structures of organic light-emitting devices based on tris-(8-hydroxyquinoline)aluminum were investigated with $Al/CaF_2$, Al/LiF, and Al-only cathodes. Similar to the Al/LiF cathode, the $Al/CaF_2$ cathode greatly improved the performance of the device over Al-only cathode. However, a photoelectron spectroscopy study revealed that despite the performance improvement, the evolution of the new peaks during $Al/CaF_2$ cathode formation closely resembled those of the Al-only cathode rather than the Al/LiF cathode.

• Proceedings of the IEEK Conference
• /
• 2000.11b
• /
• pp.37-40
• /
• 2000

This paper has been studied on characteristics of organic light-emitting device with various cathode materials. These catode materials were Al：Li(5%), Al, Cu, CsF/Al. And in these devices, HTL(hole transfer layer) was TPD and EML(emitting layer) was Alq$\sub$3/. We studied the I-V characteristics for each device. And then, the turn-on voltage of device for Al-Li(5%), Al, Cu, CsF/Al cathode were 7, 9, 13, 3V respectively. So, the CsF/Al cathode is superior to other cathode materials for I-V characteristics.

• Transactions on Electrical and Electronic Materials
• /
• v.6 no.1
• /
• pp.25-28
• /
• 2005

We have investigated the effects of hole-injection buffer layer in organic light-emitting diodes using poly(3,4-ethylenedioxythiophene):poly(stylenesulfonate)(PEDOT:PSS) in a device structure of $ITO/PEDOT:PSS/TPD/Alq_{3}/cathode$. Polymer PEDOT:PSS buffer layer was made by spin casting method. Current-voltage, luminance-voltage characteristics and efficiency of device were measured at room temperature with a variation of cathode materials; Al, LiF/Al, LiAl, and Ca/Al. The device with LiF/Al cathode shows an improvement of external quantum efficiency approximately by a factor of ten compared to that of Al cathode only device. Our observation shows that cathode is important in improving the efficiency of the organic light-emitting diodes.

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

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2005.11a
• /
• pp.277-278
• /
• 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 ($C_p$).

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

• 한국정보디스플레이학회:학술대회논문집
• /
• 2003.07a
• /
• pp.25-27
• /
• 2003

The device characteristics and the interface electronic structures of organic light-emitting devices based on /tris-(8-hydroxyquinoline)aluminum ($Alq_3$) were investigated with Al/NaF cathode. The Al/NaF cathode greatly improved the performance of the device over the Al-only cathode. A series of photoelectron spectroscopy studies on cathode structures including Al/LiF and $Al/CaF_2$ revealed that the performance enhancement originated mainly from the HOMO peak shift upon the fluoride deposition rather than the formation of the gap states

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.08a
• /
• pp.72-72
• /
• 2010

Recent development of organic solar cell approaches the level of 8% power conversion efficiency by the introduction of new materials, improved material engineering, and more sophisticated device structures. As for interface engineering, various interlayer materials such as LiF, CaO, NaF, and KF have been utilized between Al electrode and active layer. Those materials lower the work function of cathode and interface barrier, protect the active layer, enhance charge collection efficiency, and induce active layer doping. However, the addition of another step of thin layer deposition could be a little complicated. Thus, on a typical solar cell structure of Al/P3HT:PCBM/PEDOT:PSS/ITO glass, we used Li:Al alloy electrode instead of Al to render a simple process. J-V measurement under dark and light illumination on the polymer solar cell using Li:Al cathode shows the improvement in electric properties such as decrease in leakage current and series resistance, and increase in circuit current density. This effective charge collection and electron transport correspond to lowered energy barrier for electron transport at the interface, which is measured by ultraviolet photoelectron spectroscopy. Indeed, through the measurement of secondary ion mass spectroscopy, the Li atoms turn out to be located mainly at the interface between polymer and Al metal. In addition, the chemical reaction between polymer and metal electrodes are measured by X-ray photoelectron spectroscopy.

• Current Applied Physics
• /
• v.18 no.12
• /
• pp.1592-1599
• /
• 2018

The present study deals with the effect of dual cathode buffer layer (CBL) on the performance of bilayer of 4,4'-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine] (TAPC) and fullerene (C70)-based organic solar cell (OSC) with low donor concentration. OSC devices with CBLs have been fabricated using thermal vapor deposition technique. We report the use of lithium fluoride (LiF) and molybdenum trioxide ($MoO_3$) as CBLs. The insertion of LiF between C70 and aluminium (Al) electrode enhances the power conversion efficiency (PCE) of device from 1.89% to 2.47% but quenching of photogenerated excitons is observed at interface of C70 and LiF layers. Incorporation of $MoO_3$ between LiF and Al electrode further enhances PCE of device to 3.51%. This has also improved the material quality and device properties, by preventing the formation of gap states and diminishing exciton quenching.

• Korean Chemical Engineering Research
• /
• v.58 no.1
• /
• pp.52-58
• /
• 2020

Electrochemical characterization and thermal stability were investigated for MgF₂ coated LiNi_0.8Co_0.15Al_0.05O₂ cathode. The ratio of MgF₂ was controlled by 0.5, 1, 3 wt%. Cyclic voltammetry, charge-discharge profiles, rate capability, cycle life were measured for electrochemical properties. DSC analysis was measured for thermal stability. The first discharge capacities of MgF₂ coated LiNi_0.8Co_0.15Al_0.05O₂ were decreased at 0.1C-rate compared to pristine LiNi_0.8Co_0.15Al_0.05O₂. But the rate capability and cycle life of MgF₂ coated LiNi_0.8Co_0.15Al_0.05O₂ were improved at 2C-rate. In DSC analysis result, the exothermic temperature of MgF₂ coated LiNi_0.8Co_0.15Al_0.05O₂ was increased and peak height was decreased.