• 세라미스트
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• 제22권3호
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• pp.218-229
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• 2019

The development of highly efficient thermally activated delayed fluorescence (TADF) materials is an active area of recent research in organic light emitting diodes (OLEDs) since the first report by Chihaya Adachi in 2011. Traditional fluorescent materials can harvest only singlet excitons, leading to the theoretically highest external quantum efficiency (EQE) of 5% with considering about 20% light out-coupling efficiency in the device. On the other hand, TADF materials can harvest both singlet and triplet excitons through reverse intersystem crossing (RISC) from triplet to singlet excited states. It could provide 100% internal quantum efficiencies (IQE), resulting in comparable high EQE to traditional rare-metal complexes (phosphorescent materials). Thanks to a lot of efforts in this field, many highly efficient TADF materials have been developed. This review focused on recent molecular design concept and optoelectronic properties of TADF materials for high efficiency and long lifetime OLED application.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.56.2-56.2
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• 2010

국부적 후면 전극(LBC)형성은 결정질 실리콘 태양전지에서 고효율과 저가화를 동시에 달성할 수 있는 기술이다. 후면 표면 passivation과 국부적 후면 전극 형성을 통해서 후면 재결합 속도를 낮출 수 있고 이를 통해 효율향상을 기대해볼 수 있다. 본 연구에서는 PECVD를 이용한 LBC(local back contact) cell의 후면 passivation 박막을 형성하였고 접합면적에 따른 전기적 특성을 분석해 보았다. LBC cell을 위한 후면 passivation 박막은 PECVD를 이용한 ONO박막을 사용하였고, 후면 opening 형성에 etching paste를 이용하였다. Opening size는 0.4mm,0.5mm,0.7mm로 형성하여 cell을 제작하고 효율을 분석하였다. 실험결과 opening size가 0.4mm일때 전극의 접촉면적이 15.96%, 0.5mm일때 10.22%, 0.7mm일때 5.17%로 형성됨을 확인할 수 있었다. Opening size가 0.4mm일 때 cell의 효율이 가장 우수함을 IQE 및 LIV 결과를 통해 확인 할 수 있었다. 결과적으로 접촉면적이 증가함에 따라 전극에서 수집되는 carrier의 양이 증가하고 셀 효율역시 향상됨을 확인 할 수 있었다.

• 한국전기전자재료학회논문지
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• 제32권6호
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• pp.444-447
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• 2019

It was proven that the light outputs of blue GaN-based light-emitting diodes (LEDs) was seriously influenced by the application of external stress. We have simulated the wave function overlap of an electron and hole, which are significantly reduced by the development of stress. Consequently, its internal quantum efficiency decreased from 67.0% to 37.5%. To experimentally investigate the effect of stress, we designed and prepared a special zig system. By applying external tensile stress to compensate for the compressive stress innately developed in Blue LEDs, it was found that the optical output was greatly enhanced from 83.1 mcd to 117.2 mcd at a current of 100 mA, an increase of approximately 41%. In contrast, when the compressive stress is developed more by external compressive stress, we observed that the light output power was reduced from 89.0 mcd to 80.7 mcd, a decrease of approximately 9.3%.

• 한국재료학회지
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• 제24권6호
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• pp.305-309
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• 2014

When sunlight irradiates a boron-doped p-type solar cell, the formation of BsO2i decreases the power-conversion efficiency in a phenomenon named light-induced degradation (LID). In this study, we used boron-doped p-type Cz-Si solar cells to monitor this degradation process in relation to irradiation wavelength, intensity and duration of the light source, and investigated the reliability of the LID effects, as well. When halogen light irradiated a substrate, the LID rate increased more rapidly than for irradiation with xenon light. For different intensities of halogen light (e.g., 1 SUN and 0.1 SUN), a lower-limit value of LID showed a similar trend in each case; however, the rate reached at the intensity of 0.1 SUN was three times slower than that at 1 SUN. Open-circuit voltage increased with increasing duration of irradiation because the defect-formation rate of LID was slow. Therefore, we suppose that sufficient time is needed to increase LID defects. After a recovery process to restore the initial value, the lower-limit open-circuit voltage exhibited during the re-degradation process showed a trend similar to that in the first degradation process. We suggest that the proportion of the LID in boron-doped p-type Cz-Si solar cells has high correlation with the normalized defect concentrations (NDC) of BsO2i. This can be calculated using the extracted minority-carrier diffusion-length with internal quantum efficiency (IQE) analysis.

• 대한전자공학회논문지SD
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• 제48권7호
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• pp.10-16
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• 2011

본 논문에서는 고효율 고출력 무분극 GaN LED의 구현을 위하여 Mg이 도핑된 GaN spacer층 및 GaN quantum barrier(QB)층을 삽입한 구조를 제안하였다. 제안한 구조에 대한 물리적 해석을 위하여 일반적인 무분극 LED 에피구조와 본 연구에서 제안한 p-GaN spacer층 및 p-GaN QB층이 삽입된 무분극 LED 에피구조에 대해 상용화된 $SimuLED^{TM}$ 시뮬레이터를 이용하여 전기적/광학적 특성을 비교 분석하였다. 실험 결과, 본 연구에서 제안한 무분극 LED는 20 mA의 전류주입 하에서 동작전압($V_f$)이 일반적인 무분극 LED에 비해 약 3.7% 감소된 3.67 V의 전기적 특성을 갖는 것을 확인하였고, 광출력은 약 7% 향상된 2.13 mW의 광학적 특성을 갖는 구조임을 확인하였다. 또한, 내부양자효율(Internal quantum efficiency, IQE)과 광방출세기(emission peak intensity) 역시 각각 9.1% 및 170% 향상된 우수한 특성을 갖는 에피구조임을 확인하였다.