• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2008년도 International Meeting on Information Display
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• pp.1414-1417
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• 2008

Using a $Ir(ppy)_3$ doped in the TCTA:$Bepp_2$ mixed host and N- and P-doped in TCTA:$Bepp_2$ charge transport layers, an ideal energy level alignment technology is developed. A very low roll-off current efficiency of 7.4 % at a luminance of $10,000\;cd/m^2$ with this technology is demonstrated in green phosphorescent OLEDs.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.112-114
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• 2009

Charge injection at electrode-organic interfaces is key to the performance, lifetime and stability of organic electronic devices. The link between fundamental material properties and the energy-level alignment at electrode-organic interfaces will be discussed. In addition the impact of the injection barrier height-a parameterization of the energylevel alignment-on device characteristics will also be discussed.

• 진공이야기
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• 제2권2호
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• pp.12-16
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• 2015

Organic photovoltaics (OPVs) have attracted significant interest in an interdisciplinary research field for the decades as a next-generation photovoltaic device due to their unique advantages. One of requirements for OPVs having high power conversion efficiency is the favorable energy level alignment between the electrode/organic and organic/organic interfaces to manage the exciton dissociation and improve the charge transport. In this review, strategies to enhance the OPV performance by controlling the energy level alignment are discussed. The insertion of an exciton blocking layer leads to the efficient dissociation of photogenerated excitons at the donor/acceptor interface enhancing the short-circuit current density. The choice of a donor having a high ionization energy and an acceptor having a low electron affinity increases the open-circuit voltage. The insertion of an appropriate work function modifier which reduces the charge injection barrier removes the S-kink in current density-voltage characteristics of OPVs and improves the fill factor. This review would give a valuable guide to design the efficient OPV structure.

• IEIE Transactions on Smart Processing and Computing
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• 제3권2호
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• pp.83-87
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• 2014

This paper introduces a refined opportunistic interference alignment (OIA) technique that uses minimum mean square error (MMSE) detection at the receivers in multiple-input multiple-output multi-cell uplink networks. In the OIA scheme under consideration, each user performs the optimal transmit beamforming and power control to minimize the level of interference generated to the other-cell base stations, as in the conventional energy-efficient OIA. The result showed that owing to the enhanced receiver structure, the OIA scheme shows much higher sum-rates than those of the conventional OIA with zero-forcing detection for all signal-to-noise ratio regions.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.108-111
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• 2009

We have determined the electronic energy level alignment at the interface between 4,4'-bis-N-phenyl-1-naphthylamino biphenyl (NPB) and 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HAT-CN) using ultraviolet photoelectron spectroscopy (UPS). The highest occupied molecular orbital (HOMO) of 20 nm thick HAT-CN film was located at 3.8 eV below the Fermi level. Thus the lowest unoccupied molecular orbital (LUMO) is very close to the Fermi level. The HOMO position of NPB was only about 0.3 eV below Fermi level at NPB/HAT-CN interface. This enables an easy excitation of electrons from the NPB HOMO to the HAT-CN LUMO, creating electron-hole pairs across this organic-organic interface. We also study the interaction of HAT-CN with a few metallic surfaces including Ca, Cu, and ITO using UPS and ab-inito electronic structure calculation techniques.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.190.1-190.1
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• 2014

The interfacial electronic structure of a bilayer of chloroaluminum phthalocyanine (ClAlPc) and pentacene grown on indium tin oxide (ITO) has been studied using synchrotron radiation-excited photoelectron spectroscopy. The energy difference between the highest occupied molecular orbital (HOMO) level of the pentacene layer and the lowest unoccupied molecular orbital (LUMO) level of the ClAlPc layer (EDHOMO - EALUMO) was determined and compared with that of C60/pentacene bilayers. The EDHOMO - EALUMO of a heterojunction with ClAlPc was found to be 1.4 eV, while that with C60 was 1.0 eV. This difference is discussed in terms of the difference of the ionization energy of each acceptor materials. We also obtained the complete energy level diagrams of ClAlPc/pentacene/ITO and C60/pentacene/ITO, respectively.

• 한국정보통신학회논문지
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• 제19권5호
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• pp.1077-1083
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• 2015

본 논문에서는 다중 셀 상향링크 네트워크에서 합 용량을 크게 개선할 수 있는 에너지 효율적 기회적 간섭 정렬 기술을 소개한다. 각 사용자는 요구되는 신호 질을 만족하면서 타 셀 기지국에게 발생하는 간섭량을 최소화하는 측면에서 최적의 송신 벡터 설계 및 전력 제어를 수행한다. 주요 결과로써, 줄어든 간섭 레벨로 인하여 제안하는 기회적 간섭 정렬 기술은 전력 제어가 없는 기존 기회적 간섭 정렬보다 대부분의 신호 대 잡음 비 영역에서 더욱 높은 합 용량을 취득할 수 있음을 보인다. 뿐만 아니라, 제안하는 기회적 간섭 정렬 기술과 함께 수신 단에서 zero-forcing 검파 및 minimum mean square error (MMSE) 검파기를 사용할 경우 둘 사이 성능 비교를 수행하고, MMSE 검파 기반 기회적 간섭 정렬 기술이 우수한 성능을 취득할 수 있음을 보인다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.134-134
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• 2012

We investigated the interface of poly (3-hexylthiophene) (P3HT) and C61-butyric acid methylester (PCBM) by using photoelectron spectroscopy (PES). These are the most widely used materials for bulk heterojunction (BHJ) organic solar cells due to their high efficiency. Study of the BHJ interfaces is difficult because the organic films are typically prepared by spin coating in ambient conditions. This is incompatible with the interface electronic structure probes such as PES, which requires ultrahigh vacuum conditions. Study of interface requires gradual deposition of thin films that is also incompatible with the spin coating process. In this work, we used electrospray vacuum deposition (EVD) technique to deposit P3HT and PCBM in high vacuum conditions. EVD allows us to form polymer thin films onto ITO substrate in a step-wise manner directly from solutions and to use PES without exposing the sample to the ambient condition. Although the morphology of the EVD deposited P3HT films observed by optical and atomic force microscopes is quite different from that of the spin coated ones, the valence region spectra were similar. PCBM was deposited on the P3HT film in a similar manner and the energy level alignment between these two materials was studied. We discuss the relation between Voc of P3HT:PCBM solar cell and HOMO-LUMO energy offset obtained in this study.

• Applied Science and Convergence Technology
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• 제24권5호
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• pp.151-155
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• 2015

The interfacial electronic structure between zinc phthalocyanine (ZnPc) and aluminumdoped zinc oxide (AZO) substrates has been evaluated by ultraviolet photoemission spectroscopy and angle-dependent x-ray absorption spectroscopy to understanding the molecular orientation of a ZnPc layer on the performance of small molecule organic photovoltaics (OPVs). We find that the ZnPc tilt angle improves the ${\pi}-{\pi}$ interaction on the AZO substrate, thus leading to an improved short-circuit current in OPVs based on phthalocyanine. Furthermore, the molecular orientation-dependent energy level alignment has been analyzed in detail using ultraviolet photoemission spectroscopy. We also obtained complete energy level diagrams of ZnPc/AZO and ZnPc/indium thin oxide.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2005년도 International Meeting on Information Displayvol.I
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• pp.97-100
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• 2005

The recent Bistable Nematic ($BiNem{(R)}$) LCD technology presents long term bistability, high level passive matrix multiplexing and high optical quality. The BiNem device, based on anchoring breaking, needs specific low anchoring strength materials - alignment layers and liquid crystal mixtures. We present here our approach to develop nematic mixtures with wide enough temperature range and low zenithal anchoring energy.