Materials and device engineering to achieve high-performance quantum dots light emitting diodes for display applications

Quantum dots(QDs)have attracted wide attention from academia and industry because of their advantages such as high emitting efficiency,narrow half-peak width,and continuously adjustable emitting wavelength.QDs light emitting diodes(QLEDs)are expected to become the next generation commercial display technology.This paper reviews the progress of QLED from physical mechanism,materials,to device engineering.The strategies to improve QLED performance from the perspectives of quantum dot materials and device structures are summarized.

Review of blue perovskite light emitting diodes with optimization strategies for perovskite film and device structure

Perovskite light emitting diodes(PeLEDs)have attracted considerable research attention because of their external quantum efficiency(EQE)of>20%and have potential scope for further improvement.However,compared to red and green PeLEDs,blue PeLEDs have not been extensively investigated,which limits their commercial applications in the fields of luminance and full-color displays.In this review,blue-PeLED-related research is categorized by the composition of perovskite.The main challenges and corresponding optimization strategies for perovskite films are summarized.Next,the novel strategies for the design of device structures of blue PeLEDs are reviewed from the perspective of transport layers and interfacial layers.Accordingly,future directions for blue PeLEDs are discussed.This review can be a guideline for optimizing perovskite film and device structure of blue PeLEDs,thereby enhancing their development and application scope.

Efficiency analysis of a-SiC:H thin film light emitting diodes

The hole injection,the radiative recombination and the device luminescent efficiencies of amorphous silicon carbide thin film p-i-n junction light emitting diodes are quantitatively calculated,and the effect of the carrier(especially the hole) injection and recombination processes on the device luminescent characteristics are revealed.Without considering the device junction temperature,it is found that the device luminescent efficiency mainly depends on the hole injection efficiency at low field and the hole radiative recombination efficiency at high field respectively.The theoretical analyses are in well agreement with the experimental results.

The Effect of Recombination Zone Positon on the Color Temperature Performance in the Color-Tunable White Organic Light-Emitting Diode

Using a color-tunable organic light-emitting diode (CT-OLED) can accord with the circadian cycle of humans and realize healthy lighting. The variation range of the correlated color temperature (CCT) is an important parameter to measure the performance of CT-OLEDs. In this paper, the effect of changing the utilization of phosphorescent materials and the position of the recombination zone (RZ) in the device are investigated by changing the thickness of the emissive layer (EML) and the doping ratio of the host and guest materials. The results show that reducing the red phosphorescent material and improving the blue phosphorescent material can affect the change direction of CCT, but it is not enough to expand the span of CCT (ΔCCT). It is more conducive to improving ΔCCT by more reasonable regulation of the position of the main RZ in EML and the energy transfer from the blue sub-EML to the red sub-EML. Device D obtains the best electro-optic and spectral characteristics, in which the maximum ΔCCT is 5746 K (2661 - 8407 K) as the voltage changes from 3.75 V to 9.75 V, the maximum current efficiency and luminance reach 18.34 cd·A-1 and 12,100 cd·m-2, respectively.

Inorganic and Organic Solution-Processed Thin Film Devices

Thin films and thin film devices have a ubiquitous presence in numerous conventional and emerging technologies. This is because of the recent advances in nanotechnology, the development of functional and smart materials,conducting polymers, molecular semiconductors, carbon nanotubes, and graphene, and the employment of unique properties of thin films and ultrathin films, such as high surface area, controlled nanostructure for effective charge transfer, and special physical and chemical properties, to develop new thin film devices. This paper is therefore intended to provide a concise critical review and research directions on most thin film devices, including thin film transistors, data storage memory, solar cells, organic light-emitting diodes, thermoelectric devices, smart materials, sensors, and actuators. The thin film devices may consist of organic, inorganic, and composite thin layers, and share similar functionality, properties, and fabrication routes. Therefore, due to the multidisciplinary nature of thin film devices, knowledge and advances already made in one area may be applicable to other similar areas. Owing to the importance of developing low-cost, scalable, and vacuum-free fabrication routes, this paper focuses on thin film devices that may be processed and deposited from solution.

Study on Relationship between InGaAsP/InP LPE Wafer Morphology,Interface Property and Device Characteristics

Five kinds of InGaAsP/InP heterostructure materials grown with LPE have been measured by means of Auger electron analysis, X-ray double-crystal diffraction, selective etching and surface morphology analysis. The relation between crystal mismatch and interface property of such materials has been studied and the results could be understood in terms of the growth kinetics at the heterojunction interface. The comparison of the characteristics of the electronic and optoelectronic devices fabricated with the wafers under different interface properties has been carried out. And it also has been demonstrated that the wafer surface morphology changes with the compositional gradation in a certain relationship.

光生物调节诱导间充质干细胞的成骨分化

背景:间充质干细胞是从多种组织中分离出来的多能基质细胞,能够在特定的条件下分化为成骨细胞,光生物调节作为一种外部刺激能够单独或与其他诱导物联合使用加速间充质干细胞成骨分化的进程,从而为解决系列骨疾病提供新的思路。目的:综述光生物调节诱导间充质干细胞成骨分化的相关研究及机制,旨在为选用间充质干细胞作为种子细胞的骨组织工程奠定理论基础,并提出一些发展方向的建议。方法:检索中国知网、PubMed及Wed of Science数据库近年来发表的相关文献,中文检索词为“光生物调节,低功率激光,低水平激光,发光二极管,间充质干细胞,成骨分化,生物材料”;英文检索词为“Photobiomodulation,low level laser(light),light-emitting diode(LED),mesenchymal stem cell,osteogenic differentiation,Biomaterials”,最终纳入88篇文献进行分析。结果与结论:①以低水平激光和发光二极管为代表的光生物调节对于促进间充质干细胞的增殖与分化有着积极的影响。②光生物调节诱导间充质干细胞成骨分化的可行性已在细胞实验、动物实验中得到验证,一方面,光生物调节能够通过激活相关信号通路、上调成骨标志物的表达促进干细胞在体外扩增与分化;另一方面,光生物调节可以提高系统移植的干细胞体内存活率及归巢效应,缩短骨缺损愈合时间。但是光生物调节存在双相剂量效应,各项研究中激光参数、实验环境及细胞类型等要素参差不齐,使得研究结果缺乏一致性,难以推广。③光生物调节可以与生物材料、其他物理因子及药物联合使用加速干细胞成骨分化的进程。④总之,光生物调节因其无创、高效且无明显副反应等优势在医疗领域的应用逐渐广泛;近年来,其在骨组织工程中的作用也逐渐凸显,为骨缺损等疾病的治疗提供了新策略,后续研究应进一步探索光生物调节的标准化治疗参数。

Highly Efficient Hybrid White Tandem Organic Light-Emitting Diodes with MoO3 Layer

Electroluminescence （EL） characteristics have been studied for a hybrid tandem white organic light emitting diode （OLED） with a blue emitting fluorescent EL1 unit based on BCzVBi and a yellow emitting phosphorescent EL2 unit based on （fbi）2Ir（acac）, where a MoO3 layer is inserted between EL1 and EL2 units as charge generation layer （CGL）. Maximum current and power efficiencies of 68.1 cd/A and 29.2 lm/W were obtained, respectively, while the current and power efficiencies at luminance of 1000 cd/m2 were 68.0 cd/A and 24.6 lm/W. The yellow emission appears from about 4.5 V firstly, while the blue emission starts to appear from about 5.4 V. It was found that charge generation from CGL of MoO3/NPB bilayer occurred at high voltages of above 5.4 V but not at low voltages below 5.2 V.

Tandem organic light-emitting diodes with buffermodified C_(60)/pentacene as charge generation layer

Buffer-modified C_(60)/pentacene as charge generation layer(CGL) is investigated to achieve effective performance of charge generation. Undoped green electroluminescent tandem organic light-emitting diodes(OLEDs) with multiple identical emissive units and using buffer-modified C_(60)/pentacene organic semiconductor heterojunction(OHJ) as CGL are demonstrated to exhibit better current density and brightness, compared with conventional single-unit devices. The current density and brightness both can be significantly improved with increasing the thickness of Al. However, excessive thickness of Al seriously decreases the transmittance of films and damages the interface. As a result, the maximum current efficiency of 1.43 cd·A^(-1) at 30 mA ·cm^(-2) can be achieved for tandem OLEDs with optimal thickness of Al. These results clearly demonstrate that Cs_2CO_3/Al is an effective buffer for C_(60)/pentacene-based tandem OLEDs.

有机电致发光器件及显示驱动研究进展

经过30多年的发展,得益于对高效有机半导体材料、新型器件结构、器件工作机理的深入理解以及产业界坚持不懈的工程探索,有机发光二极管(Organic light‑emitting diodes,OLEDs)的综合性能取得了突破性进展,并成功实现了商业化应用,OLEDs新型显示已成为新一代信息技术的先导性支柱产业。本文将从OLEDs器件角度阐述有机电致发光器件以及显示驱动的研究进展,首先结合光电器件性能提升介绍OLED的基本器件结构演变过程,随后系统性重点阐述现阶段产业上广泛使用以及极具应用前景的器件结构,包括p‑i‑n OLEDs器件结构、叠层器件结构、非掺杂器件结构,最后简述OLEDs显示驱动技术,以期为相关科研工作者提供一些有益的参考。

A New Conducting Polymer Electrode for Organic Electroluminescence Devices

Conducting polymer polydimethylsiloxane （PDMS） is studied for the high performance electrode of organic electroluminescence devices. A method to prepare the electrode consisting of a SiC thin film and PDMS is investigated. By using ultra thin SiC films with different thicknesses, the organic electroluminescence devices are obtained in an ultra vacuum system with the model device PDMS/SiC/PPV/Alq3, where PPV is poly para-phenylene vinylene and Alq3 is tris（S-hydroxyquinoline） aluminium. The capacitance voltage （C - V）, capacitance-frequency （C - F）, current-voltage （I - V）, radiation intensity-voltage （R - V） and luminance eFficiency-voltage （E - V） measurements are systematically studied to investigate the conductivity, Fermi alignment and devices properties in organic semiconductors. Scanning Kelvin probe measurement shows that the work function of PDMS/SiC anode with a 2.5-nm SiC over layer can be increased by as much as 0.28eV, compared to the conventional ITO anode. The result is attributed to the charge transfer effect and ohmic contacts at the interface.

Evaluation of current and temperature effects on optical performance of InGaAlP thin-film SMD LED mounted on different substrate packages

The relationship between the photometric, electric, and thermal parameters of light-emitting diodes（LEDs） is important for optimizing the LED illumination design. Indium gallium aluminium phosphide（InGaAlP）-based thin-film surface-mounted device（SMD） LEDs have attracted wide attention in research and development due to their portability and miniaturization. We report the optical characterization of InGaAlP thin-film SMD LED mounted on FR4, 2 W, and 5 W aluminum（Al） packages. The optical and thermal parameters of LED are determined at different injection currents and ambient temperatures by combining the T3ster（thermal transient tester） and TeraL ED（thermal and radiometric characterization of power LEDs） systems. Analysis shows that LED on a 5 W Al substrate package obtains the highest luminous and optical efficiency.

III-Nitride-Based Quantum Dots and Their Optoelectronic Applications

During the last two decades, III-nitride-based quantum dots(QDs) have attracted great attentions for optoelectronic applications due to their unique electronic properties. In this paper, we first present an overview on the techniques of fabrication for III-nitride-based QDs. Then various optoelectronic devices such as QD lasers, QD light-emitting diodes(LEDs), QD infrared photodetectors(QDIPs) and QD intermediate band(QDIB) solar cells(SCs) are discussed. Finally, we focus on the future research directions and how the challenges can be overcome.

基于热活化敏化荧光的蓝光材料与器件研究进展

有机发光二极管(Organic light emitting diode,OLED)作为新一代显示技术已经成功产业化,但兼具高效率和长寿命的蓝光OLED仍是亟待解决的问题。近年来,采用热活化延迟荧光(Thermally activated delayed fluorescence,TADF)材料敏化窄光谱荧光染料的热活化敏化荧光(TADF sensitized fluorescence,TSF)机制日益受到广泛关注。随着发光材料和器件结构的不断创新,基于该机制的蓝光OLED器件性能显著提升。本文围绕稳定高效蓝光敏化剂分子的设计开发,综述了近年来蓝光TSF器件在效率与寿命方面的进展,并进一步讨论了未来的发展目标以及面临的挑战。

YAG:Ce玻璃陶瓷选择性激光烧结制备及其发光性能

荧光玻璃陶瓷结合了荧光粉优异的发光性能和玻璃基质良好的热导率及热稳定性的特点,已在高功率白光LED乃至激光照明领域引起了广泛的关注。本文采用一种选择性激光(CO_(2)激光器)烧结技术,制备了YAG∶Ce荧光玻璃陶瓷,并研究了其荧光发光性能以及构筑的白光LED的器件性能。与传统的重熔融或固相烧结方法不同,选择性激光烧结技术仅对局部加热且升/降温速率大,因此该方法具有节能和快速的特点。研究表明,选用适当的激光功率(24 W)、扫描速度(135 mm/s)和扫描间隔(9μm)等参数,可制备出形貌较好的YAG∶Ce荧光玻璃陶瓷;经过630℃热处理1 h消除应力后,其呈现出Ce^(3+)离子典型的4f→5d能级跃迁对应的宽带激发光谱(峰值为340 nm和455 nm)以及5d→4f能级跃迁对应的宽带发射光谱(峰值为570 nm),量子效率达82%;与450 nm蓝光LED芯片(3.11 V,0.30 A)组合后,可实现92 lm的白光输出,流明效率为98 lm/W,显色指数为69,色温为5 001 K,色坐标为(0.34,0.35)。以上结果表明,该方法在制备荧光玻璃陶瓷中具有重要的应用潜力。

高成品率和平整度的GaN基Micro LED芯片激光剥离工艺的研究

使用波长248 nm的准分子激光器实现了GaN基微型发光二极管(Micro LED)的大面积激光剥离(LLO)。分离器件所需要的临界激光能量密度为800~835 mJ·cm^(-2),分离的器件完好无损,分离表面光滑,残余应力为0.0714 GPa,均方根粗糙度仅为0.597 nm,远低于目前报道的LLO方法分离表面。该研究为实现高质量、高效率的GaN基Micro LED芯片的制备提供了一种有前景的思路,对柔性GaN基器件的制备具有一定意义。

基于量子点和纳米线复合体系的低维柔性光发射器件

柔性自发光器件是当前照明和显示领域的前沿课题。相比有机发光二极管,无机半导体具有更稳定的物理化学性质,但晶态无机薄膜不具有良好柔韧性,因此,低维纳米线阵列结构成为柔性器件研究新的突破方向。铯铅卤化物钙钛矿量子点具有高发光量子产率,将钙钛矿量子点作为荧光层分散在纳米线阵列中,可以利用钙钛矿材料的高荧光效率,实现可见波段柔性器件。首先制备了氧化锌(ZnO)/氧化镁(MgO)纳米线阵列异质结构,在柔性锌箔基片上构建了金属/绝缘体/半导体异质结光发射器件,实现了源自ZnO纳米线的本征紫外发射和电泵浦紫外随机激光。进而采用纳米线异质结作为短波长激发源、钙钛矿量子点作为荧光层,实现了柔性荧光型暖白光原型器件。

有机发光二极管老化机制

有机发光二极管(OLEDs)因在照明和显示领域的巨大潜在应用备受人们关注。在过去的三十年里,OLED器件的效率和寿命有了很大的提高,但对于商业应用而言提高器件寿命仍然是亟待解决的问题之一。为了进一步提升器件稳定性,则需要深入地研究OLED内部存在的老化机理。本文以小分子和聚合物OLEDs为例,综述了两种器件的老化机制。概括了OLED的一些外在和内在老化机制,并介绍了小分子和聚合物OLEDs老化机理的研究进展。对于小分子OLEDs,有研究提出其老化机理是激子与极化子的相互作用,形成陷阱导致器件老化。另一种理论认为激子与极化子的作用诱导分子聚集,促进界面老化。而对于聚合物OLEDs老化机理是激子与空穴相互作用,诱导空穴陷阱产生,导致了亮度、效率损失和驱动电压上升的现象。同时综述了目前一部分延长器件寿命的方案,为后续开发效率更高、寿命更长的OLED器件提供积极作用。

近紫外白光LED用铕(Ⅲ)配合物发光材料的应用研究进展

白光发光二极管(LED)具有高效、环保等优点,可广泛应用于照明领域。本文以稀土配合物为切入点,介绍了发光材料的发光原理,对相关的稀土配合物发光材料及其制备方法进行了总结,阐明了配合物的荧光强度主要受到发射态的能量、激发三重态到稀土离子共振态的能量转移效率、配体对紫外光的吸收强度等因素的影响,并就如何提高铕配合物的性能,扩大在LED上的应用进行了展望。

Light-emitting diodes based on colloidal silicon quantum dots

Colloidal silicon quantum dots （Si QDs） hold great promise for the development of printed Si electron- ics. Given their novel electronic and optical properties, colloidal Si QDs have been intensively investigated for op- toelectronic applications. Among all kinds of optoelectronic devices based on colloidal Si QDs, QD light-emitting diodes （LEDs） play an important role. It is encouraging that the performance of LEDs based on colloidal Si QDs has been significantly increasing in the past decade. In this review, we discuss the effects of the QD size, QD sur- face and device structure on the performance of colloidal Si-QD LEDs. The outlook on the further optimization of the device performance is presented at the end.