• Title/Summary/Keyword: Cathode interface

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Cathode interface engineering for stable and efficient organic light-emitting diodes

  • Qiu, Yong;Duan, Lian;Li, Yang
    • 한국정보디스플레이학회:학술대회논문집
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    • 2007.08b
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    • pp.1199-1202
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    • 2007
  • The improvement of the electron injection is of critical importance for obtaining efficient and stable organic light-emitting diodes(OLEDs). Here, we report some of our recent results on the development of new cathode interlayer materials for OLEDs. Some of our new materials show performance superior to that of LiF.

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Improvement of Electrochemical Properties and Thermal Stability of a Ni-rich Cathode Material by Polypropylene Coating

  • Yoo, Gi-Won;Son, Jong-Tae
    • Journal of Electrochemical Science and Technology
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    • v.7 no.2
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    • pp.179-184
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    • 2016
  • The interface between the surface of a cathode material and the electrolyte gives rise to surface reactions such as solid electrolyte interface (SEI) and chemical side reactions. These reactions lead to increased surface resistance and charge transfer resistance. It is consequently necessary to improve the electrochemical characteristics by suppressing these reactions. In order to suppress unnecessary surface reactions, we coated cathode material using polypropylene (PP). The PP coating layer effectively reduced the SEI film that is generated after a 4.3 V initial charging process. By mitigating the formation of the SEI film, the PP-coated Li[(Ni0.6Co0.1Mn0.3)0.36(Ni0.80Co0.15Al0.05)0.64)]O2(NCS) electrode provided enhanced transport of Li+ ions due to reduced SEI resistance (RSEI) and charge transfer resistance (Rct). The initial charge and discharge efficiency of the PP-coated NCS electrode was 96.2 % at a current density of 17 mA/g in a voltage range of 3.0 ~ 4.3 V, whereas the efficiency of the NCS electrode was only 94.7 %. The presence of the protective PP layer on the cathode improved the thermal stability by reducing the generated heat, and this was confirmed via DSC analysis by an increased exothermic peak.

Cathode Microstructure Control and Performance Improvement for Low Temperature Solid Oxide Fuel Cells (저온 고체산화물 연료전지용 공기극 미세구조 제어 및 성능개선)

  • Kang, Jung-Koo;Kim, Jin-Soo;Yoon, Sung-Pil
    • Journal of the Korean Ceramic Society
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    • v.44 no.12
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    • pp.727-732
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    • 2007
  • In order to fabricate a highly performing cathode for low-temperature type solid oxide fuel cells working at below $700^{\circ}C$, electrode microstructure control and electrode polarization measurement were performed with an electronic conductor, $La_{0.8}Sr_{0.2}MnO_3$ (LSM) and a mixed conductor, $La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_3$(LSCF). For both cathode materials, when $Sm_{0.2}Ce_{0.8}O_2$ (SDC) buffer layer was formed between the cathode and yttria-stabilized zirconia (YSZ) electrolyte, interfacial reaction products were effectively prevented at the high temperature of cathode sintering and the electrode polarization was also reduced. Moreover, cathode polarization was greatly reduced by applying the SDC sol-gel coating on the cathode pore surface, which can increase triple phase boundary from the electrolyte interface to the electrode surface. For the LSCF cathode with the SDC buffer layer and modified by the SDC sol-gel coating on the cathode pore surface, the cathode resistance was as low as 0.11 ${\Omega}{\cdot}cm^2$ measured at $700^{\circ}C$ in air atmosphere.

Use of Self Assembled Monolayer in the Cathode/Organic Interface of Organic Light Emitting Devices for Enhancement of Electron Injection

  • Manna, U.;Kim, H.M.;Gowtham, M.;Yi, J.;Sohn, Sun-young;Jung, Dong-Geun
    • 한국정보디스플레이학회:학술대회논문집
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    • 2005.07b
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    • pp.1343-1346
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    • 2005
  • Self assembled monolayers (SAM) are generally used at the anode/organic interface to enhance the carrier injection in organic light emitting devices, which improves the electroluminescence performance of organic devices. This paper reports the use of SAM of 1-decanethiol (H-S(CH2)9CH3) at the cathode/organic interface to enhance the electron injection process for organic light emitting devices. Aluminum (Al), tris-(8-hydroxyquionoline) aluminum (Alq3), N,N'-diphenyl-N,N'-bis(3 -methylphenyl)-1,1'- diphenyl-4,4'-diamine (TPD) and indium-tin-oxide (ITO) were used as bottom cathode, an emitting layer (EML), a hole-transporting layer (HTL) and a top anode, respectively. The results of the capacitancevoltage (C-V), current density -voltage (J-V) and brightness-voltage (B-V), luminance and quantum efficiency measurements show a considerable improvement of the device performance. The dipole moment associated with the SAM layer decreases the electron schottky barrier between the Al and the organic interface, which enhances the electron injection into the organic layer from Al cathode and a considerable improvement of the device performance is observed. The turn-on voltage of the fabricated device with SAM layer was reduced by 6V, the brightness of the device was increased by 5 times and the external quantum efficiency is increased by 0.051%.

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Characteristic Improvements of Organic Light Emitting Diodes By Using Co-Evaporated Cathodes

  • Kwak, Y.H.;Lee, Y.S.;Park, J.H.;Choi, Jong-Sun
    • 한국정보디스플레이학회:학술대회논문집
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    • 2002.08a
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    • pp.710-713
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    • 2002
  • In order to improve the power efficiency of multi-layer organic light emitting diodes (OLEDs), electron injection into ETL(electron transport layer) from cathode at the interface between ETL and cathode was enhanced by interposing a proper electron injection layer at the interface. The HTL(hole transport layer) and ETL materials used were N, N'diphenyl- N, N' - bis(3-methylphenyl-1, 1'- biphenyl - 4, 4 'diamine (TPD) and tris (8-hydroxyquinoline) aluminum ($Alq_3$) respectively. Cathodes using co-evaporated Al-CsF, Al-KF, and Al-NaF composites are adopted to enhance the electrical and optical properties of OLEDs. OLEDs with alkaline metal-doped cathode show a luminance of as high as 35,000 cd/$m^2$, and external quantum efficiency about 1.35 %. In addition, they show higher power efficiency at all bias conditions and good reproducibility.

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Performance degradation of SOFC caused by increase of polarization resistance for the cathode during long-term test (공기극 분극 저항 증가에 따른 SOFC 단전지 성능 감소에 관한 연구)

  • Park, Kwang-Jin;Bae, Joong-Myeon
    • 한국신재생에너지학회:학술대회논문집
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    • 2009.06a
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    • pp.349-352
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    • 2009
  • In this study, the relation between the performance degradation of SOFC single cell and the increase of polarization resistance for the cathode is investigated. $Pr_{0.3}Sr_{0.7}Co_{0.3}Fe_{0.7}O_3$(PSCF3737, $19.4{\times}10^{-6}K^{-1}$) and $Gd_{0.1}Ce_{0.9}O_2$ (CGO91, $12{\times}10^{-6}K^{-1}$) are used as a cathode and an electrolyte, respectively. The polarization resistance of cathode is increased due to the delamination caused by thermal expansion coefficient difference. The voltage drop with 10%/1000h decline rate occurs during long-term, when the interface between the cathode and the electrolyte is delaminated due to TEC difference.

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Impedance spectroscopy analysis of polymer light emitting diodes with the LiF buffer layer at the cathode/organic interface (LiF 음극 버퍼층을 사용한 폴리머의 효율 향상에 관한 임피던스 분석)

  • Kim, H.M.;Jang, K.S.;Yi, J.;Sohn, Sun-Young;Park, Kuen-Hee;Jung, Dong-Geun
    • 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 ($C_p$).

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Overview of Interface Engineering for Organic Solar Cells (유기태양전지 계면 기술 동향)

  • Kim, Gi-Hwan
    • Journal of Adhesion and Interface
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    • v.22 no.4
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    • pp.113-117
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    • 2021
  • Among the next-generation solar cells, organic solar cells using organic materials are a key energy production device for the future energy generation devices, and have recently been receiving a lot of attention with rapid growth. To improve the efficiency of organic solar cells, interfacial engineering technology has been widely applied. In particular, it is widely used to improve device efficiency through energy level control by using interface engineering on the anode and cathode, which are positive electrodes, and to ultimately utilize interface engineering for tandem organic solar cells to derive excellent electrical and optical performance to produce high-performance devices. In this article, we will summarize and introduce recent research trends on interfacial engineering used in organic solar cells, and discuss the method of manufacturing high-performance organic solar cells.

Electrochemical stability of La0.6Sr0.4Co0.2Fe0.8O3-δ as a cathode for SOFC

  • Oh, Mi-Young;Jeong, Yong-Hoon;Oh, Se-Woong
    • Journal of the Korean institute of surface engineering
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    • v.49 no.6
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    • pp.498-506
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    • 2016
  • Electrochemical measurement using a LSCF6428 electrode was performed to estimate the oxygen potential gradient in the electrode layer and a long time stability test was performed by applied potential to learn the overpotential effect on the LSCF6428 electrode. By fitting the observed impedance spectra, it was obtained that the amount of faradic current decreased with distance from cathode/electrolyte interface. Oxygen potential gradient was estimated to occur within 1 um region from the cathode/electrolyte interface at an oxygen partial pressure of 10-1 bar. The segregation of cation rich phases in the LSCF6428 electrode suggests that kinetic decomposition took place. However, impedance response after applying the potential showed no changes in the electrode compared with before applying potential. The obtained results suggest that segregation of a secondary phase in a LSCF6428 cathode is not related to performance degradation for solid oxide fuel cells (SOFCs).

Review of interface engineering for high-performance all-solid-state batteries (계면 제어를 기반으로 한 고성능 전고체 전지 연구)

  • Insu, Hwang;Hyeon Jeong, Lee
    • Journal of Industrial Technology
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    • v.42 no.1
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    • pp.19-27
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    • 2022
  • This review will discuss the effort to understand the interfacial reactions at the anode and cathode sides of all-solid-state batteries. Antiperovskite solid electrolytes have received increasing attention due to their low melting points and anion tunability which allow controlling microstructure and crystallographic structures of this material system. Antiperovskite solid electrolytes pave the way for the understanding relationship between critical current density and mechanical properties of solid electrolytes. Microstructure engineering of cathode materials has been introduced to mitigate the volume change of cathode materials in solid-state batteries. The hollow microstructure coupled with a robust outer oxide layer effectively mitigates both volume change and stress level of cathode materials induced by lithium insertion and extraction, thus improving the structural stability of the cathode and outer oxide layer, which results in stable cycling performance of all-solid-state batteries.