• Journal of the Optical Society of Korea
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• 제20권1호
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• pp.29-35
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• 2016

This paper deals with a design method and capacity loss of an efficient multi-level modulation scheme for dimmable visible light communications (VLC) systems that use light-emitting diodes (LEDs) with efficiency droop. To this end, the impact of such an impairment on dimmable VLC is addressed with respect to multi-level modulations based on pulse-amplitude modulation (PAM) via data-rate optimization formulation.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 추계학술발표대회
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• pp.13.1-13.1
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• 2011

Photoelectrochemical solar cells such as dye-sensitized cells (DSSCs), which exhibit high performance and are cost-effective, provide an alternative to conventional p-n junction photovoltaic devices. However, the efficiency of such cells plateaus at 11~12%, in contrast to their theoretical value of 33%. The majority of research has focused on improving energy conversion efficiency of DSSC by controlling nanostructure and exploiting new materials in photoelectrode consisting of semiconducting oxide nanoparticles and a transparent conducting oxide electrode (TCO) [1-5]. In this presentation, we introduce inverse opal-based scattering layers containing highly crystalline anatase nanoparticles and their feasibility for use as bi-functional light scattering layer is discussed in terms of optical reflectance and charge generation properties as a function of optical wavelength. A new ITO nanowire-based photoelecrode is also introduced and its unique charge collection property is presented, demonstrating potential use for highly efficient charge collection in DSSC.

• 생물환경조절학회지
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• 제25권3호
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• pp.139-145
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• 2016

본 연구의 목적은 폐쇄형 식물생산시스템에서 세가지 혼합 LED와 형광등에서 자란 적치마 상추의 생육과 광이용효율을 비교하는 것이다. 18일간 육묘한 적치마상추묘를 적색(R, 655nm), 청색(B, 456nm), 녹색(G, 515nm), 백색(W, 456nm + 558nm)의 혼합 LED(R:B=8:2, R:W:B=8:1:1, R:G:B=8:1:1)와 형광등이 설치된 폐쇄형 식물생산시스템에 정식하였다. 형광등에서 자란 상추는 모든 LED 처리에 비해 유의적으로 높은 엽형지수를 보였다. 지상부와 지하부 생육에서 LED 처리간 유의적 차이를 보이지 않았으나, 모든 LED 처리가 형광등에 비해 약 34% 지상부 생체중의 증가를 유도시켰다. 한편, 정식 후 4주차에 형광등의 총 소비 전력은 145kW인 반면, LED 처리구들에서 형광등의 약 1/3배인 54kW를 나타냈다. LED 처리구들의 건물중에 대비한 광 이용 효율은 약 34mg/W였으며, 이는 형광등 보다 약 3.5배 높은 값이었다. 결론적으로, 본 연구는 식물 생산 시스템에서 적절한 조합의 LED 조사는 형광등에 비해 상추 생장을 증진시킬 수 있으며 추가적으로 에너지 절감을 통해 광이용효율도 극대화 할 수 있음을 보여주었다.

• 한국전기전자재료학회논문지
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• 제26권10호
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• pp.745-753
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• 2013

Performance of organic light-emitting diodes incorporating microlens array was simulated using a Light Tools software. Use of microlens array can help the light to escape out of the device. We simulated a reference device that is consisted of reflection layer, emissive layer, and flat transparent substrate. And in this reference device, outcoupled efficiency of 22% was obtained. Several shapes of microlens were applied such as hemisphere, trapezoid, cone, and rectangular parallelepiped. The results showed the improvement of outcoupled efficiency of the device with microlens compared to that of the reference one. And from the analyses of the simulated data, the obtained appropriate shape of microlens is hemisphere, and the improvement of the device with hemispherical lens is 57% higher than that of the reference one.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2002년도 International Meeting on Information Display
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• pp.766-769
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• 2002

We have seen the effects of hole-injection buffer layer in organic light-emitting diodes using copper phthalocyanine(CuPc), poly(vinylcarbazole)(PVK), and Poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate)(PEDOT:PSS) in a device structure of ITO/buffer/TPD/$Alq_3$/Al. Polymer PVK and PEDOT:PSS buffer layer was made using spin casting method and the CuPc layer was made using thermal evaporation. Current-voltage characteristics, luminance-voltage characteristics and efficiency of device were measured at room temperature with a thickness variation of buffer layer. We have obtained an improvement of the external quantum efficiency by a factor of two, four, and two and half when the CuPc, PVK, and PEDOT:PSS buffer layer are used, respectively. The enhancement of the efficiency is attributed to the improved balance of holes and elelctrons due to the use of hole-injection buffer layer. The CuPc and PEDOT:PSS layer functions as a hole-injection supporter and the PVK layer as a hole-blocking one.

• 한국광과학회:학술대회논문집
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• 한국광과학회 1997년도 학술대회지
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• pp.41-41
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• 1997

• Journal of Ecology and Environment
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• 제45권1호
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• pp.54-61
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• 2021

Background: The sunfleck is an important light environmental factor for plants that live under the shade of trees. Currently, the smartfarm has a system that can artificially create these sunfleks. Therefore, it was intended to find optimal light conditions by measuring and analyzing photosynthetic responses of Eutrema japonica (Miq.) Koidz., a plant living in shade with high economic value under artificial sunflecks. Results: For this purpose, we used LED pulsed light as the simulated sunflecks and set the light frequency levels of six chambers to 20 Hz, 60 Hz, 180 Hz, 540 Hz, 1620 Hz, and 4860 Hz of a pulsed LED grow system in a plant factory and the duty ratio of the all chambers was set to 30%, 50%, and 70% every 2 weeks. We measured the photosynthetic rate, transpiration rate, stomatal conductance, and substomatal CO2 partial pressure of E. japonica under each light condition. We also calculated the results of measurement, A/Ci, and water use efficiency. According to our results, the photosynthetic rate was not different among different duty ratios, the transpiration rate was higher at the duty ratio of 70% than 30% and 50%, and stomatal conductance was higher at 50% and 70% than at 30%. In addition, the substomatal CO2 partial pressure was higher at the duty ratio of 50% than 30% and 70%, and A/Ci was higher at 30% than 50% and 70%. Water use efficiency was higher at 30% and 50% than at 70%. While the transpiration rate and stomatal conductance generally tended to become higher as the frequency level decreased, other physiological items did not change with different frequency levels. Conclusions: Our results showed that 30% and 50% duty ratios could be better in the cultivation of E. japonica due to suffering from water stress as well as light stress in environments with the 70% duty ratio by decreasing water use efficiency. These results suggest that E. japonica is adapted under the light environment with nature sunflecks around 30-50% duty ratio and low light frequency around 20 Hz.

• 한국광학회:학술대회논문집
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• 한국광학회 2008년도 하계학술발표회 논문집
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• pp.61-63
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• 2008

Parallel femtosecond laser processing using a computer-generated hologram (CGH) displayed on a liquid crystal spatial light modulator (LCSLM) is demonstrated. The use of the LCSLM enables to perform an arbitrary and variable patterning. This holographic femtosecond laser processing has advantages of high throughput and high light-use efficiency. A critical issue is to precisely control the intensities of the diffraction peaks of the CGH. We demonstrate some methods for the control of the diffraction peaks. We also demonstrate the laser processing with two-dimensional and three-dimensional parallelism.

• 한국전기전자재료학회논문지
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• 제24권5호
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• pp.427-431
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• 2011

Hybrid $SiO_2-TiO_2$ photoelectrode with different type of layers was investigated in dye-sensitized solar cells (DSSC). Use of a thin layer of nanocrystalline $TiO_2$ would imply reduction in the amount of dye coverage, however, lower amount of dye in the thin films would imply fewer electron generation upon illumination. So, thus, it becomes necessary to include a $SiO_2-TiO_2$ layer for increase light harvesting effect such that the lower photon conversion due to thin layer could be compensated. In this paper reports the use of transparent high surface area $TiO_2$ layer and an additional $SiO_2-TiO_2$ layer, thus ensuring adequate light harvesting in these devices. The best solar conversion efficiency 6.6% under AM 1.5 was attained with a multi-layer structure using $TiO_2$ layer/$SiO_2-TiO_2$ layer/$TiO_2$ layer for the light harvesting and this had resulted to about 44% increase in photocurrent density of dye-sensitized solar cells.

• 원예과학기술지
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• 제32권4호
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• pp.493-498
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• 2014

본 연구는 완전제어형 식물공장에서 선형 지수 함수를 이용하여 common ice plant의 생육과 수량 모델을 개발하고자 수행되었다. 식물공장 유형은 완전제어형 식물공장형태로 인공광원은 삼파장 형광등을 사용하였으며, 광주기는 12시간 일장주기였다. 광도는 $200{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$로 조절하였다. 수경재배시스템은 3단으로 구성된 박막수경(NFT)시스템이었다. 식물공장내 온도, 상대습도와 이산화탄소 농도는 ON/OFF 제어하였다. 선형 지수 함수를 사용한 common ice plant의 정식 후 일수, 적산온도 및 적산일사량에 따른 엽면적, 단위 면적당 지상부 생체중과 건물중 및 광사용효율은 선형 지수적인 형태들을 보였다. 개체당 지상부 생체중과 개체당 지상부 건물중간의 관계는 직선적인 관계를 보였으며, 정식 후 30일째 common ice plant의 광사용효율(light use efficiency)은 $3.3g{\cdot}MJ^{-1}$이었다. 결론적으로, 선형 지수 함수는 완전제어형 식물공장에서 common ice plant의 생육과 수량을 정량적으로 예측하는데 유용한 함수로 사용될 수 있었다.