High-efficiency LED Research Articles

Modular design of a high-efficiency LED headlamp system based on freeform reflectors

Abstract A modular of the LED headlamp system based on freeform reflectors is proposed. Glare suppression and optical design are taken into account during the module design. The proposed module consists of six LEDs and each of them has a freeform reflector correspondingly, which is constructed based on the light energy maps and Snell’s Law. Through lighting up different LEDs, the high-beam light and the low-beam light can be switched conveniently. With the proposed method, a module is designed and LUW HWQP LED source whose chip size is 1.0 mm×1.0 mm is adopted for the simulation. Results demonstrate that the lighting distribution can well fulfill the requirements of ECE R112 regulation without any other lenses, shields or baffles. Furthermore, the total optical efficiency can reach up to 80.29% and 81.16% for the low-beam light and high-beam light respectively.

A High Power InGaN‐LED on an m‐Plane GaN Substrate

SUMMARYGrowing demands for reduction of energy consumption and environmental impact are rapidly leading to the spread of solid‐state LED lighting with low power consumption and high reliability. To meet these demands, we are developing high efficiency and high power LEDs on GaN substrates. A high optical output power of 1.23 W at 1 A was obtained by using the technologies of epitaxial growth of high‐quality m‐plane InGaN on GaN substrates and low contact resistance electrodes. The m‐plane InGaN‐LED realized a quite small external‐efficiency droop of about 20% up to 500 A/cm2, while major droop occurs in polar c‐plane (0001) InGaN LEDs.

New bioinspired hole injection/transport materials for highly efficient solution-processed phosphorescent organic light-emitting diodes

A new concept to supramolecular assembly of existed functional polymers, capable of forming network-like organizational clusters through multiple hydrogen-bonding interactions has been exploited. In this paper, a new adenine-based poly(triphenylamine-carbazole) (PTC-A) has been prepared which exhibits a high self-complementary ability in solution and solid states owing to the formation of adenine–adenine (A–A) pairs by induced hierarchical self-assembly. Comparing with uracil-substituted PTC sample (PTC-U), PTC-A presents a much higher thermal stability, electrochemical stability and solvent-resistance ability due to the formation of the more stable physically cross-linking structure. When the PTC-A is utilized as a hole injection/transport layer in a trilayer OLED device, a remarkable improvement in performance relative to the control PTC and PTC-U under similar experimental conditions has been achieved. Further comparison with a control device using a conventional PEDOT:PSS, the efficiency of the solution-processed phosphorescent PLED device with PTC-A is significantly higher than those of PTC-U and PEDOT:PSS-based devices. Thus, PTC-A represents the next-generation hole injection/transport material for high efficiency LED device and low-cost fabrication process.

高发光效率的LED光电器件的结构设计和性能研究

高发光效率的LED光电器件的结构设计和性能研究

T09 高効率LED排熱回収型低温度差スターリングエンジンの開発(模型スターリングエンジン並びに教材用熱音響機器(2))

T09 高効率LED排熱回収型低温度差スターリングエンジンの開発(模型スターリングエンジン並びに教材用熱音響機器(2))

A Study on Nanosilver Adhesive for LED Light Application

This study proposes a development for the nanosilver adhesive, which is applicable to high efficiency LED light. The important issue of LED light is heat exhaust from LED. Generally, the middle area of LED light is increased up to 380K. Therefore, the bottleneck between LED chip and heat sink are caused by high temperature. In this work, the adhesive material between LED Chip and heat sink was newly developed for improvement of bottleneck. The nanosilver was adopted to solve heat problem of chip on board package for LED light. In order to evaluate the performance of the nanosilver adhesive, the thermal analysis was performed. Moreover both adhesive performance and heat exhaust were verified through the prototype test. From the experimental test results, it is found that the developed nanosilver adhesive has the high performance.

Study on the Development of High-efficiency, Long-life LED Fog Lamps for the Used Car Market

LED lighting,considered to be a new growth industry, has attracted a great deal of attention due to its higher illumination and longer life time than existing light sources. In this study, high-efficiency and long-life LED fog lamps for automobiles were developed, which can substitute the existing 27 W halogen fog lamps for a used car market. For this purpose, the number of LED modules, the body, heat sink, and the output of the fog lamp were first optimized through a numerical analysis. Then, a 10 W-class LED fog lamp was prototyped based on the optimized numerical model, and the performance of the fog lamp was successfully verified through the experiments.

가로등에 적합한 고효율 멀티채널 LED 조명 구동장치 설계

LED 조명 구동장치는 150W 이상에서 효율과 발열문제가 있고 W(와트)수가 다른 조명기기를 교체하는데 불편함이 있다. 본 논문에서는 멀티채널 LED 조명 구동장치를 드라이버 연동형 구조의 전원시스템과 멀티채널 구조형태의 드라이버 회로내장형으로 설계하였다. 본 개발품은 전원효율 93% 이상 및 역율 0.98 이상의 자동 제어 컨버터 구조로써 드라이버 연동형 구조의 고효율 LED 조명 구동장치와 자기보상방식의 자기최적화 구조의 드라이버다. 따라서, 본 논문은 THD 10% 이하와 기존 컨버터 대비 중량이 40% 이상 감소하였다. LED light driving device has problems in efficiency and heating at higher than 150W. In addition, there is inconvenience in replacing the lighting device to another when W is not the same as the previous one. In this paper, a multi-channel LED light driver, driver embedded driver circuit in a multi-channel structure with a power system in the driver-interlocking structure was designed. With the auto control converter structure with a power efficiency above 93% and power factor above 0.98, the weight of the high efficiency LED lighting-actuating device in driver-interlocking structure, a driver in self-calibrating self-optimization structure. In this paper, at below 10% THD, the existing converter contrast weight was reduced by 40% or more.

Design of an LED-based headlamp low-beam system using combined prisms

An effective high-efficiency LED headlamp system for automotive low-beam lighting which consists of parabolic reflector, compound lenses and combined prisms, is introduced in this paper. Using a single, high-brightness LED, the illumination requirements for a headlamp low beam specified by UNECE regulation ‘Addendum 111: Regulation No. 112 Revision 2’ can be achieved. On the test screen at a distance of 25 m, simulation results as well as testing results for the prototype meet the requirements of the UNECE regulation for all specified regions and key points.

Anisotropic strain relaxation and the resulting degree of polarization by one- and two-step growth in nonpolar a-plane GaN grown on r-sapphire substrate

Anisotropic strain relaxation and the resulting degree of polarization of the electronic transition in nonpolar a-plane GaN using one- and two-step growth are studied. By using two-step growth, a slower coalescence and a longer roughening-recovery process lead to larger anisotropic strain relaxation, a less striated surface, and lower densities of basal stacking fault (BSF) and prismatic stacking fault (PSF). It is suggested that anisotropic in-plane strains, surface striation, and BSF and PSF densities in nonpolar a-GaN are consequences of the rate of coalescence, the period of roughening-recovery process, and the degree of anisotropic strain relaxation. In addition, the two-step growth mode can enhance the degree of polarization of the electronic transition. The simulation results of the k⋅p perturbation approach show that the oscillator strength and degree of polarization of the electronic transition strongly depend on the in-plane strains upon anisotropic in-plane strain relaxation. The research results provide important information for optimized growth of nonpolar III-nitrides. By using two-step growth and by fabricating the devices on the high-quality nonpolar free-standing GaN substrates, high-efficiency nonpolar a-plane InGaN LEDs can be realized. Nonpolar a-plane InGaN/GaN LEDs can exhibit a strongly polarized light to improve the contrast, glare, eye discomfort and eye strain, and efficiency in display application.

Photo- and electroluminescence from semiconductor colloidal quantum dots in organic matrices: QD-OLED

The results are reported of an experimental study of samples of organic light-emitting diodes (OLEDs) with luminescent layers fabricated on the basis of two types of CdSe/CdS/ZnS semiconductor quantum dots (QDs) with average CdSe core diameters of 3.2 and 4.1 nm and the same overall diameters of 6.5 nm. The dependences of the LED efficiency on the applied voltage are determined. Assumptions are made about ways of optimizing the design of high-efficiency LEDs.

실리콘 리플렉터를 적용한 고효율 고출력 LED 패키지 개발

실리콘 리플렉터를 적용한 고효율 고출력 LED 패키지 개발

Design of High Power RGB White Light Emitting Diodes

In this paper, thermal performance of RGB white LED packages was optimized by thermal simulation using the Finite Volume method. A Monte Carlo photon simulation method was utilized for the analysis of optical performance of LED in quantitative terms. It was found that the distribution of RGB chips has great effect both on the thermal and optical performance of the RGB white LEDs. The tilted angle, material of the reflection cup, and the shape of encapsulant were found to be the key factors which determine the extraction efficiency of LED package. It is demonstrated that the combination of optical and thermal simulation provides a comprehensive optimization approach for a design of high efficient RGB white LED package.

Improved ohmic contact of Ga-Doped ZnO to p-GaN by using copper sulfide intermediate layers

Copper sulfide (CuS) was used as the intermediate layer to build ohmic contact of Ga-Doped ZnO (GZO) transparent conduction layer (TCL) to p-GaN. The CuS and GZO layers were prepared by thermal evaporation and RF magnetron sputtering, respectively. Although the GZO-only contacts to p-GaN exhibit nonlinear behavior, ohmic contact with a specific contact resistance of 1.6×10−2Ωcm2 has been realized by inserting 3nm CuS layer between GZO and p-GaN. The optical transmittance of CuS/GZO film was measured to be higher than 80% in the range of 450–600nm wavelength. The possible mechanism for the ohmic contact behavior can be attributed to the increased hole concentration of p-GaN surface induced by CuS films after annealing. The forward voltage of LEDs with CuS/GZO TCL has been reduced by 1.7V at 20mA and the output power has been increased by 29.6% at 100mA compared with LEDs without CuS interlayer. These results indicated that using CuS intermediate layer could be a potential ohmic contact method to realize high-efficiency LEDs.

High-efficiency InGaN-based LEDs grown on patterned sapphire substrates using nanoimprinting technology

This study employed roller imprint lithography and dry etching to fabricate patterned sapphire substrates (PSSs) of convex-shape with features of various heights. A soft polymer, polydimethylsiloxane (PDMS), was used as a mold to duplicate the pattern of a hard silicon template. The imprinted material was spin deposited onto a PDMS mold and transferred to the sapphire substrate using roller imprinting equipment. Inductive coupled plasma (ICP) etching was then used to fabricate the PSS. After epitaxial growth and chip processing, the current–voltage characteristics and light output of various LEDs were measured. The results demonstrate that the PSS process did not detract from the electrical properties of the LEDs; in fact, the output power of the proposed PSS LEDs was 25–30% greater than that of conventional LEDs. Simulation results show that PSS LEDs with structures of various heights would enhance optical efficiency in a manner similar to that demonstrated in these experiments.

Design of an optical transmission WDM link using plastic optical fibers

ABSTRACTIn this paper we present the design of an optical transmission system, using plastic optical fiber (POF), which operates in the visible range of the electromagnetic spectrum. The optical signals are generated by modulated visible LEDs, transmitted through POF and at the reception end a pin-pin photodetector is implemented. A computer simulation tool dedicated to the analysis of optical circuits was used for preliminary analysis of the optical system. The performance of the optical link was analyzed by BER prediction variation on the transmission rate. The tested optical system was assembled using high efficiency LEDs of the same wavelengths, a commercial POF and a pin-pin photodetector based on a-SiC:H/a-SI:H. This detector behaves as an optical filter with controlled wavelength sensitivity. Different optical signals, obtained by adequate modulation of LED optical sources, were coupled into the POF and the combined optical signal at the fiber termination was directed onto the photodetector active area. The output photocurrent was measured with and without optical bias. Results compare the use of a pin-pin transducer device in free space and in a POF transmission link.

Improving Light Extraction Efficiency of GaN-Based LEDs by Al$_{\bm x}$Ga$_{{\bf 1}{\bm -}{\bm x}}$N Confining Layer and Embedded Photonic Crystals

The interaction of low-order modes with photonic crystals (PhCs) has been a promising technique to increase light extraction efficiency (LEE) of LEDs. In this paper, numerical simulations based on the finite-difference time-domain method were carried out to explore different mechanisms that can effectively improve this interaction. The results showed that deeply etched PhCs have inefficient light extraction since they would decrease the effective thickness of the unetched layer and cut off some guided modes. By applying the Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> N confining layer, the distribution of guided modes was changed. The cap layer mode was isolated from the GaN buffer, and larger LEE was achieved. Furthermore, dramatic increments with oscillations were found in the LEE by using embedded PhCs. Resonances of the Bloch mode localized within these PhCs, which caused the oscillations, were further modified by a shallow Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> N confining layer. With the optimized parameters, over eightfold increment in LEE was achieved. In addition, dislocations caused by higher Al content and thicker Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> N layer were avoided. This proposed structure could be a very promising candidate for high extraction efficiency LEDs.

A Loss-Adaptive Self-Oscillating Buck Converter for LED Driving

A loss-adaptive self-oscillating buck converter is proposed for high-efficiency and low-cost LED driving. It consists of a self-oscillating unit composed of bipolar junction transistors (BJTs)-type self-oscillating unit, a loss-adaptive BJT driving unit, and a low-loss peak-current sensing unit. In this paper, its operation principle including a loss-adaptive BJT-driving scheme and a low-loss peak-current sensing method is introduced. For experimental verification, a prototype LED driver was implemented with some cheap components and devices for a 24-V lighting system to drive up to six LEDs. The test results show that the prototype LED driver could successfully start up itself and operate highly efficiently in steady state. In order to improve the performance of the proposed buck converter, a useful pulse-width modulation (PWM) LED dimming function is discussed for the future study.

High Efficiency LED Module with 3D Bending Machine

Abstract- In this paper, a bending machine for tuning optical design of LED module is proposed. The tuning is done by changing the bending angles of each package on a given module with the help of automatic control program. Luminous intensity distribution can be controlled by adjusting the light emission path, which in turn can be implemented as changing the bending angles of individual LED packages on the module. The proposed machine is capable of bending packages to specified angles with errors less than 0.1°. Three-dimensional light distribution for bent package LED modules is also studied based on various application scenarios so that each scenario can have diversified luminous intensity distribution resulting in higher uniformity and better luminance quality. The machine has several advantages, including quick bending, high accuracy, and great customizability. These advantages make the machine meet the requirements of automatic mold forming.

Formation of a low-resistance and high reflectivity reflector on p-type GaN with a AgAl Ohmic contact

In this study, we investigate the effect of the Al composition of a AgAl alloy reflector deposited on a p-GaN layer for use in a high-efficiency GaN flip-chip light-emitting diode (FCLED) or n-type sideup vertical LEDs. When the Al composition was 3%, the AgAl reflector showed low resistance, high reflectance and thermally stable ohmic contact properties. For an Al composition of 3% in the AgAl reflector, the optical output power was improved by 50%, and the current-voltage characteristic was improved compared to that for a Ag reflector. These results clearly indicate that a AgAl layer on p-GaN constitutes a promising reflector and ohmic scheme for achieving high-brightness FCLEDs and vertical LEDs.