• Korean Journal of Materials Research
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• v.30 no.8
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• pp.421-425
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• 2020

A transparent quantum dot (QD)-based light-emitting diode (LED) with silver nanowire (Ag NW) and indium-tin oxide (ITO) hybrid electrode is demonstrated. The device consists of an Ag NW-ITO hybrid cathode (-), zinc oxide, poly (9-vinylcarbazole) (PVK), CdSe/CdZnS QD, tungsten trioxide, and ITO anode (+). The device shows pure green-color emission peaking at 548 nm, with a narrow spectral half width of 43 nm. Devices with hybrid cathodes show better performances, including higher luminance with higher current density, and lower threshold voltage of 5 V, compared with the reference device with a pure Ag NW cathode. It is worth noting that our transparent device with hybrid cathode exhibits a lifetime 9,300 seconds longer than that of a device with Ag NW cathode. This is the reason that the ITO overlayer can protect against oxidization of Ag NW, and the Ag NW underlayer can reduce the junction resistance and spread the current efficiently. The hybrid cathode for our transparent QD LED can applicable to other quantum structure-based optical devices.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.7B
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• pp.606-612
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• 2012

Visible light communications (VLC) uses modern solid-state LEDs to broadcast information. Emerging white-light LEDs allows the combination of lighting and optical wireless communication in one optical source. In this paper, a new LED lighting using one-chip-type white LED is proposed for efficient illumination and optical wireless communications. Performance analysis such as horizontal illuminance, 3-dB cut-off frequency, inter-symbol interference, signal-to-noise ratio and bit-error rate shows the effects of the shapes of LED lighting. Performance of the proposed LED lighting under the existence of obstacles is superior to that of the existing LED lighting in illumination and optical wireless communication.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.3
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• pp.8-21
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• 2015

Technology for electric lighting has been evolving from Incandescent Lamp(IL) through Fluorescent Lamp(FL) and currently to Solid State Lighting(SSL) such as LED for more than 130 years of time. However, it took more than 100 years until the transition from IL to FL across overall society. That is because the transition is the Socio-Technical Transition(STT) which involves various social elements. This study investigated and analyzed the theories regarding STT, and applied the Multi-Level Perspective(MLP) theory to the case of electric lighting. A qualitative contents analysis was used with secondary data as research method, and the analyzed result was visualized based on the frame of MLP theory. The STT of electric lighting from IL to FL took place as the order of Technical Niche, Socio-Technical Regime and Landscape. Specifically, in Technical Niche level: Establishing Market Niche, Price-Performance Improvement, Learning Process and Support of Powerful Group took place. In Socio-Technical Regime level: Changes in Social Network, Changes in Technology and Changes in Rules. In Landscape level: Macro-Political Development, Socio-Economic Trends and Macro-Economic Trends took place in consecutive order.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1666-1669
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• 2006

Plextronics develops conductive polymer technology (trademarked $Plexcore^{TM}$) that will enable the broad market commercialization of printed electronic devices. This talk will emphasize advances to our $Plexcore^{TM}$ HIL technology - a soluble non-acidic hole injection layer (HIL) technology for OLEDs . which is designed to dramatically improve device efficiency and lifetime of flat panel displays and solid state white-lighting.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1577-1582
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• 2006

Tandem OLED structures formed by connecting two or more low-voltage electroluminescent units (stacks) are effective for achieving high efficiency at low current density as well as long operational lifetime. We have fabricated white emitting tandem structures with two or three low-voltage white-emitting stacks using transparent organic "PN"-type connectors. Three- stack white tandem structures with efficiency greater than 24 cd/A at D65 and operational stability of about 110,000 h. (extrapolated) at $1000\;cd/m^2$ have been demonstrated. With a stacked structure, the power consumption for displays using an RGBW format can be reduced by 25% compared to previously described formulations. We have also fabricated advanced white tandem structures where the color gamut (NTSC x,y ratio) has been improved to greater than 70% using standard color filters. The white OLEDs can also be used to increase the colorrendering index CRI (>80%), an important consideration for solid-state lighting.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.108-108
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• 2012

High-performance GaN-based light emitting diodes (LEDs) with high efficiency and excellent reliability have been of technological importance forapplications in full color display, automotive lighting, and solid state lighting. To realize high-performance and excellent-reliability LEDs, various technologies such as surface texturing, transparent conducting oxide, surface Plasmon, highly p-conduction layer, current blocking layer, photon-enhanced layer, and nanostructures have been extensively investigated. Among them, advanced core technologies based on how to suppress surface leakage and current crowding, how to enhance current injection efficiency and output power, and how to resist electrostatic damage will be displayed and discussed using our reported and preliminary results. New approaches like integrated LEDs will be also introduced and discussed.

• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.443-444
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• 2012

최근 각광받고 있는 반도체 발광 소자를 이용한 고체 상태 광원(Solid State Lighting)은 기존 광원에 비해 고효율이어서 에너지 절약적 측면에서 대두되고 있다. 점광원인 LED에 비해 면광원인 OLED는 두께를 얇게 구현할 수 있고, 다양한 모양으로 광원의 구현이 가능하다. 따라서, 본 논문에서는 효율적인 OLED 조명 구동을 위해 넓은 입력전압 범위를 지니는 Buck-Boost 컨버터를 제안한다.

• Korean Journal of Materials Research
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• v.27 no.6
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• pp.312-317
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• 2017

In the construction of a white LED, the region of the red emission is a very important factor. Red light emitting materials play an important role in improving the color rendering index of commercial lighting. These materials also increase the color gamut of display products. Therefore, the development of novel phosphors with red emission and the study of color tuning are actively underway to improve product quality. In the present study, heuristic algorithms were used to search for phosphors capable of increasing the color rendering index and color gamut. Using a heuristic algorithm, the phosphors that were identified were $SrGe_4O_9:Mn^{4+}$ and $BaGe_4O_9:Mn^{4+}$. Emission spectra study confirmed that these phosphors emit light in the deep red wavelength region, which can fulfill the requirement for the improvement in color rendering index and color gamut for a white LED.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.3
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• pp.194-200
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• 2020

Perylene bisimide derivatives are developed for red organic phosphor because of their advantages, such as excellent luminous efficiency and high thermal stability. Despite these advantages, they have poor solubility characteristics in organic solvents and short emission wavelength as red organic phosphor for hybrid light-emitting diodes (LEDs). In this study, we prepared terrylene bisimide using a coupling reaction and swallow-tail imide group, which has excellent solubility. The structures and properties of swallow-tail terrylene bisimide (9C) were analyzed using ¹H-nuclear magnetic resonance (¹H-NMR), Fourier-transform infrared (FT-IR), UV/Vis spectroscopy, and thermal gravimetric analysis (TGA). The maximum absorption wavelength of (9C) in the UV/Vis spectrum was 647 nm, and the maximum emission wavelength was 676 nm. In the TGA, (9C) demonstrated good thermal stability with less than 5 wt% weight loss up to 415℃. In the solubility test, (9C) has a good solubility of more than 5 wt% in chloroform and dichloromethane. When the compounds (9C) were mixed with PMMA (polymethly methacrylate), the films showed peaks at 680 nm in the PL spectra. The results verify the suitability of (9C) as a red organic phosphor for hybrid LEDs.

• Journal of the Semiconductor & Display Technology
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• v.18 no.1
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• pp.10-14
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• 2019

In this study, we synthesized two $Y_3Al_5O_{12}:Ce^{3+}$ phosphors ($7{\mu}m$-sized and $2{\mu}m$-sized YAG) with different sizes by controlling particles sizes of starting materials of the phosphors for white LED. In the smaller one ($2{\mu}m$-sized YAG), its photoluminescence intensity in the reflective mode was 63 % that of the bigger one ($7{\mu}m$-sized YAG); the quantum efficiencies were 93 % and 70 % for the smaller and the bigger ones. Two kinds of white LED packages with the same color coordinates were fabricated with a blue package (chip size $53{\times}30$) and two phosphors. The luminous flux of the white LED package with the smaller YAG phosphor was 92 % of that with the bigger one, indicating that the quantum efficiency of phosphor dispersed inside LED package was higher than that of the pure powder. It was consistently confirmed by the optical simulation (LightTools 6.3). It is notable according to the optical simulation that the white LED with the smaller phosphor showed 24 % higher luminous efficiency. If the smaller one had the same quantum efficiency as the bigger one (~93 %). Therefore, it can be suggested that the higher luminous efficiency of white LED can be possible by reducing the particle size of the phosphor along with maintaining its similar quantum efficiency.