Blue perovskite LEDs

Metal halide perovskite light-emitting diodes (PeLEDs)show great potential in ultra-high-definition displays,due to their narrowband emission,wide color gamut (～140％),and cost-effective solution processability[1]M.Thanks to scientists' tremendous efforts,the external quantum efficiencies (EQEs)for the state-of-the-art PeLEDs emitting near-infrared and green light have reached 21.6％[2] and 23.4％[3],respectively.However,blue PeLEDs,as one of the essential technologies for perovskite-based high-resolution monitors and white light-ing,are still inferior to their red and green counterparts.Blue emission is usually achieved by using dimensional engineer-ing (quantum confinement) or composition engineering(mixed halides,e.g.,mixed Br/Cl) strategies.For example,quasi-two-dimensional (2D) perovskites,nanocrystals (e.g.,quantum dots,QDs) or nanoplates,give blue emission due to quantum confinement effects.However,achieving pure-blue(465-475 nm) and deep-blue (420-465 nm) light from quasi-2D perovskites is challenging[4],while ultra-small QDs and nanoplates suffer from high surface trap density and poor sta-bility[5].For PeLEDs based on mixed Br/Cl perovskites,the emis-sion peak can be tuned easily,but these perovskites face the disadvantages of phase separation and deep energy-level Cl vacancies[4].     

High Efficiency Blue Organic LEDs Achieved By an Integrated Fluorescence–Interlayer–Phosphorescence Emission Architecture

This paper presents a new strategy to develop efficient organic light‐emitting devices (OLEDs) by doping fluorescent‐ and phosphorescent‐type emitters individually into two different hosts separated by an interlayer to form a fluorescence–interlayer–phosphorescence (FIP) emission architecture. One blue OLED with FIP emission structure comprising p‐bis(p‐N,N‐diphenylaminostyryl)benzene (DSA‐Ph) and bis[(4,6‐di‐fluorophenyl)‐pyridinate‐N,C²']picolinate (FIrpic) exhibiting a peak luminance efficiency of 15.8 cd A^?1 at 1.54 mA cm^?2 and a power efficiency of 10.2 lm W^?1 at 0.1 mA cm^?2 is successfully demonstrated. The results are higher than those of typical phosphorescent OLEDs with a single emission layer by 34% and 28%, respectively. From experimental and theoretical investigations on device performance, and the functions of the used emitters and interlayer, such enhancement should ascribe to the appropriate utilization of the two types of emitters. The fluorescent emitter of DSA‐Ph is used to facilitate the carrier transport, and thus accelerate the generation of excitons, while the phosphorescent emitter of FIrpic could convert the generated excitons into light efficiently. The method proposed here can be applied for developing other types of red, green, and white OLEDs.     

提高基于粉浆法的功率型白光LEDs发光效率的研究

基于水溶性感光胶的自光LEDs平面涂层技术,在蓝光LED芯片表面上得到了可控的荧光粉层．采用降低粉浆中ADC的浓度和提高荧光粉的含量两种措施,减少Cr^3＋在433．6和620nm两处吸收对器件出光效率的影响;新配制的粉浆在暗室中静置3～5h,既可以提高器件的出光效率同时又避免了暗反应带来的影响;在蓝光LED表面上得到粉层后,再涂覆硅胶层,由于硅胶的折射率与粉层的更接近,不但使出光色调偏向蓝光区域而且有更多光子出射,光通量由未加硅胶层时的44．8～59lm提高到了79．4～84．9lm．     

DC Current-Induced Rollover of Illumination Efficiency of GaN-Based Power LEDs

Pulse drive currents were utilized to investigate dc current-induced rollover of illumination efficiency of GaN-based power light-emitting diodes (LEDs). By using the pulse drive currents, we can separate the effects that junction temperature and current injection have on dc current-induced rollover of illumination efficiency of GaN-based power LEDs. Comparing the measurement results obtained from pulse and dc drive currents, we verified that junction temperature and current injection were the major causes of dc current-induced rollover of illumination efficiency of power LEDs.     

提高基于粉浆法的功率型白光LEDs发光效率的研究

基于水溶性感光胶的白光LEDs平面涂层技术,在蓝光LED芯片表面上得到了可控的荧光粉层.采用降低粉浆中ADC的浓度和提高荧光粉的含量两种措施,减少Cr3+在433.6和620nm两处吸收对器件出光效率的影响;新配制的粉浆在暗室中静置3～5h,既可以提高器件的出光效率同时又避免了暗反应带来的影响;在蓝光LED表面上得到粉层后,再涂覆硅胶层,由于硅胶的折射率与粉层的更接近,不但使出光色调偏向蓝光区域而且有更多光子出射,光通量由未加硅胶层时的44.8～59 lm提高到了79.4～84.9 lm.     

大功率LED效率特性分析与驱动方案设计

考察了大功率LED量子效率衰落问题的研究进展并检测和比较了当前市场不同产品的大功率LED性能,随着LED效率-电流特性的逐渐改善,其最高效率所对应驱动电流开始超过额定电流。由此提出LED的矩形波脉冲驱动策略,驱动电路中MOS晶体管栅极由低频(200～800Hz)矩形脉冲调制高频(～40kHz)脉冲产生的间歇式PWM脉冲串来控制,在输出端滤除高频成分后得到接近于矩形波的低频脉冲电流输出。在调节驱动电路的电流工作点以达到负载LED最高发光效率工作点同时,约束输出脉冲峰值电流与占空比以保证LED驱动电流的平均值恒定。     

Improved Efficiency in Blue Phosphorescent Organic Light‐Emitting Devices Using Host Materials of Lower Triplet Energy than the Phosphorescent Blue Emitter

Data from a series of phosphorescent blue organic light‐emitting devices with emissive layers consisting of either 4,4′‐bis(N‐carbazolyl)‐2,2′‐biphenyl (CBP):6% bis[(4,6‐difluorophenyl)pyridinato‐N,C²](picolinato)iridium(III) (FIrpic) or bis(9‐carbazolyl)benzene (mCP):6% FIrpic show that the triplet energy of the hole and electron transport layers can have a larger influence on the external quantum efficiency of an operating device than the triplet energy of the host material. A maximum external quantum efficiency of 14% was obtained for CBP:6% FIrpic devices which is nearly double all other published CBP:6% FIrpic results. A new host material, 4‐(diphenylphosphoryl)‐N,N‐di‐p‐tolylaniline (DHM‐A2), which has a triplet energy lower than that of FIrpic is also reported. Devices fabricated using DHM‐A2 show improved performance (lower drive voltage and higher external quantum efficiency) over devices using 4‐(diphenylphosphoryl)‐N,N‐diphenylaniline (HM‐A1), a high performance ambipolar DHM‐A2 analogue with a triplet energy greater than FIrpic. Nearly 18% external quantum efficiency was obtained for the DHM‐A2:5% FIrpic devices. The results suggest modified design rules for the development of high performance host materials: more focus can be placed on molecular structures that provide good charge transport (ambipolarity for charge balance) and good molecular stability (for long lifetimes) rather than first focusing on the triplet energy of the host material.     

低损伤ICP刻蚀技术提高GaN LED出光效率

首先分析了在制作GaN基LED时,采用干法刻蚀技术会对材料的表面和量子阱有源区造成损伤,影响了GaN基LED的内量子效率。针对这个问题,研究实验采用感应耦合等离子反应刻蚀(ICP-RIE)技术,分别选择了氯气/三氯化硼(Cl2/BCl3)气体体系和氯气/氩气(Cl2/Ar)气体体系,通过优化射频功率、ICP功率、气体流量以及相应的真空度,得到了良好的刻蚀端面,对于材料造成的损伤较低,得到更好的I-V特性。实验结果表明,采用低损伤的偏压功率刻蚀后制作的LED器件,出光功率提升一倍以上,同时采用Cl2/Ar气体体系,改善了器件的I-V特性,有效提高了LED的出光效率。     

ICP刻蚀p-GaN表面微结构GaN基蓝光LED

采用基于Cl2/Ar/BCl3气体的感应耦合等离子体(ICP)刻蚀技术制作了p-GaN表面具有直径3 μm、周期6 μm的二维圆孔微结构GaN基蓝光LED,研究了刻蚀深度对光荧光(PL)和发光二极管(LED)光电特性的影响.结果表明,刻蚀深度为25 nm的表面微结构,与传统平面结构相比,其PL增强了42.8%;而采用ITO作为透明电极的LED,在20 mA注入电流下,正面出光增强了38%、背面出光增强了10.6%,同时前向电压降低了0.6 V,反向漏电流基本不变.     

Resonant Contactless Energy Transfer With Improved Efficiency

This paper describes the theoretical and experimental results achieved in optimizing the application of the series loaded series resonant converter for contactless energy transfer. The main goal of this work is to define the power stage operation mode that guarantees the highest possible efficiency. The results suggest a method to select the physical parameters (operation frequency, characteristic impedance, transformer ratio, etc.) to achieve that efficiency improvement. The research clarifies also the effects of the physical separation between both halves of the ferromagnetic core on the characteristics of the transformer. It is shown that for practical values of the separation distance, the leakage inductance, being part of the resonant inductor, remains almost unchanged. Nevertheless, the current distribution between the primary and the secondary windings changes significantly due to the large variation of the magnetizing inductance. An approximation in the circuit analysis permits to obtain more rapidly the changing values of the converter parameters. The analysis results in a set of equations which solutions are presented graphically. The graphics show a shift of the best efficiency operation zone, compared to the converter with an ideally coupled transformer. Experimental results are presented confirming that expected tendency.     

A 1.8-GHz CMOS Power Amplifier Using a Dual-Primary Transformer With Improved Efficiency in the Low Power Region

A 1.8-GHz CMOS power amplifier for a polar transmitter is implemented with a 0.18- RF CMOS process. The matching components, including the input and output transformers, were integrated. A dual-primary transformer is proposed in order to increase the efficiency in the low power region of the amplifier. The loss induced by the matching network for the low-output power region is minimized using the dual-primary transformer. The amplifier achieved a power-added efficiency of 40.7% at a maximum output power of 31.6 dBm. The dynamic range was 34 dB for a supply voltage that ranged from 0.5 to 3.3 V. The low power efficiency was 32% at the output power of 16 dBm.     

有机多层白光发光二极管

以四苯基二胺衍生物(TPD)为空穴传输材料,以蓝光染料酚基吡啶铍(BePP2)、黄光染料红荧烯(Rubrene)、绿光染料8-羟基喹啉铝(Alq3)分别为蓝、绿、红三基色染料,采用多层结构制备了有机多层白光发光二极管.该白光器件的色坐标为( 0.33, 0.36)(在7V下),接近等能点白光( 0.33, 0.33);该器件在17V下的亮度可以达到3000cd/m2,流明效率为 0.3 lm/w,是目前报道的比较好的结果.     

有机多层白光发光二极管

以四苯基二胺衍生物（ＴＰＤ）为空穴传输材料,以蓝光染料酚基吡啶铍（ＢｅＰＰ２）、黄光染料红荧烯（Ｒｕｂｒｅｎｅ）、绿光染料８－羟基喹啉铝（Ａｌｑ３）分别为蓝、绿、红三基色染料,采用多层结构制备了有机多层白光发光二极管．该白光器件的色坐标为（０．３３,０．３６）（在７Ｖ下）,接近等能点白光（０．３３,０．３３）;该器件在１７Ｖ下的亮度可以达到３０００ｃｄ／ｍ２,流明效率为０．３ｌｍ／Ｗ,是目前报道的比较好的结果     

Blue flip-chip AlGaInN LEDs with removed sapphire substrate

Characteristics of AlGaInN LEDs with removed sapphire substrate are studied. To remove the substrate from a finished LED crystal mounted by the flip-chip method onto a silicon wafer, the laser lift-off technique was used. To raise the light output efficiency, a scattering profile was formed on the n-GaN surface by ion etching in a Cl₂: Ar gas mixture. This resulted in the 25–30% increase in the external quantum efficiency of LEDs. The LEDs fabricated in this way demonstrate stable operation at drive currents of up to 300 mA with an optical power as high as 110 mW.     

倒装结构大功率蓝光LEDs的研制

从器件制作角度入手，对基于Ⅲ族氮化物的功率型蓝光LEDs结构和电极体系进行了优化设计。采用梳状结构、高反电极体系及倒装焊技术，研制出大功率蓝光LEDs，在350mA工作电流下，工作电压为3．3～3．5V，输出功率达137．71mW，反向5V电压下的漏电流小于1μA。     

聚合物液体LED和有机激光

描述了两种液态聚合物LED器件特性及发光机制,一种是溶液LED（SLED）,活性层为溶液介质;另一种是凝胶介质,其中含有溶剂,二者发光机理都产生于电产生的化学发光（ECL）。前者载流子是带电的聚合物链,靠近阴极处被氧化的聚合物分子及靠近阳极的被还原的分子分别向对电极移动时复合产生辐射跃近;后者仅是在阴极处被氧化的溶剂分子,在凝胶中迁移时与在阳极附近被还原的高分子链相遇而产生辐射复合。它们与固体聚合物LED和EL发光机制有些不同。另外,描述了聚合物激光及Bell实验室研制的电注入激光现象。     

GaN基蓝光LED关键技术进展

以高亮度GaN基蓝光LED为核心的半导体照明技术对照明领域带来了很大的冲击,并成为目前全球半导体领域研究和投资的热点。本文首先综述了GaN基材料的基本特性,分析了GaN基蓝光LED制程的关键技术如金属有机物气相外延,P型掺杂,欧姆接触,刻蚀工艺,芯片切割技术,介绍了目前各项技术的工艺现状,最后指出了需要改进的问题,展望了末来的研究方向。     

Improved Reliability and ESD Characteristics of Flip-Chip GaN-Based LEDs With Internal Inverse-Parallel Protection Diodes

In this letter, a GaN/sapphire light-emitting diode (LED) structure was designed with improved electrostatic discharge (ESD) performance through the use of a shunt GaN ESD diode connected in inverse-parallel to the GaN LED. Thus, electrostatic charge can be discharged from the GaN LED through the shunt diode. We found that the ESD withstanding capability of GaN/sapphire LEDs incorporating this ESD-protection feature could be increased from several hundreds up to 3500 V in the human body model. Furthermore, flip-chip (FC) technology was also used to produce ESD-protected LEDs to further improve light output power and reliability. At a 20-mA current injection, the output power of the FC LEDs showed an improvement of around 60%. After a 1200-h aging test, the luminous intensities of the FC LEDs featuring an internal ESD-protection diode decreased by 4%. This decay percentage was far less than those of non-FC LEDs     

A CLL Resonant Asymmetrical Pulsewidth-Modulated Converter With Improved Efficiency

In this paper, a CLL resonant tank fed by an asymmetrical pulsewidth-modulated (APWM) drive train is presented as an attractive option for low-power point-of-use power supplies used in telecom applications. This configuration can guarantee zero-voltage switching (ZVS) for an extended input voltage range of 35-75 V, while significantly reducing the associated conduction loss present in existing topologies. Proper resonant tank design will ensure efficient operation over the entire working range by maintaining ZVS for all line and load conditions, as well as minimizing the conduction loss by decreasing the circulating-current commensurate with load. Analysis of the converter topology is conducted, and a design procedure is presented. Experimental results from a 25-W 48-V/2.5-V proof-of-concept prototype are presented to validate the analysis and simulation results and to highlight the merits of the proposed topology. The proposed converter is shown to provide a 7%-14% efficiency improvement over a reference topology.     

高效率B类功率GaAs FET放大器

B类工作、谐波调谐和改进器件是提高功率GaAsFET放大器功率附加效率的三个重要因素。本文综述了国外B类功率GaAsFET放大器的现状。