The strategies for preparing blue perovskite light-emitting diodes

Metal halide perovskites have attracted tremendous interest due to their excellent optical and electrical properties,and they find many promising applications in the optoelectronic fields of solar cells,light-emitting diodes,and photodetectors.Thanks to the contributions of international researchers,significant progress has been made for perovskite light-emitting diodes(Pero-LEDs).The external quantum efficiencies(EQEs)of Pero-LEDs with emission of green,red,and near-infrared have all exceeded 20%.However,the blue Pero-LEDs still lag due to the poor film quality and deficient device structure.Herein,we summarize the strategies for preparing blue-emitting perovskites and categorize them into two:compositional engineering and size controlling of the emitting units.The advantages and disadvantages of both strategies are discussed,and a perspective of preparing high-performance blue-emitting perovskite is proposed.The challenges and future directions of blue PeroLEDs fabrication are also discussed.

A Method to Obtain Auger Recombination Coefficient in an InGaN-Based Blue Light-Emitting Diode

We propose and demonstrate to derive the Auger recombination coefficient by fitting efficiency-current and carrier lifetime-current curves simultaneously, which can minimize the uncertainty of fitting results. The obtained Auger recombination coefficient is 1.0×10^(-31) cm^6 s^(-1) in the present sample, which contributes slightly to efficiency droop effect.

Developments and challenges ahead in blue perovskite light-emitting devices

Recently,perovskite light-emitting diodes(Pe LEDs)have developed rapidly in the green,red,and nearinfrared light emissions,owing to the unique optoelectronic characteristics of halide perovskites,such as high carrier mobility,narrow emission linewidths,high photoluminescence quantum yield,as well as bandgap tunability.However,the efficiency improvement in blue(especially deep-blue)Pe LEDs is still inferior to other analogs,which severely restricts the Pe LED applications.Here,we systematically summarize the substantial progress in the performance of blue Pe LEDs based on different blue perovskite candidates,and recent advances from three aspects(i.e.,the sky-blue,pure-blue,and deep-blue light emissions).Then,we point out several challenges existing in deep-blue Pe LEDs,such as the effect of Cl-ions incorporation,spectral instability,ion migration,and the difficulty of charge injection,and highlight the strategies to improve device efficiency,to motivate further research and development of blue Pe LEDs.

A Novel Application of Lithium Heteropoly Blue as Non-aqueous Electrolyte in Polyacenic Semiconductor-Li Secondary Batteries

Lithium heteropoly blue(Li 5PW Ⅵ 10 W Ⅴ 2O 40 ) was used as a non aqueous electrolyte in the polyacenic semiconductor (PAS) Li secondary battery instead of LiClO 4. The properties of the PAS Li secondary battery, especially the effect of Li 5PW Ⅵ 10 W Ⅴ 2O 40 on the capacity, the cycle property and the self discharging of the battery have been investigated. The results indicate that not only Li 5PW Ⅵ 10 W Ⅴ 2O 40 can overcome the disadvantages of LiClO 4, which is apt to explode when heated or rammed, but also the PAS Li secondary battery assembled with the novel electrolyte has a larger capacity and smaller self discharging than that assembled with LiClO 4. Therefore, it is believed that lithium heteropoly blue is a better and novel electrolyte for the PAS secondary battery and exhibits significant and practical application.

Zn杂质诱导GaInP/AlGaInP红光半导体激光器量子阱混杂的研究

在GaAs基GaInP/AlGaInP单量子阱结构外延片上分别使用磁控溅射设备生长ZnO薄膜和等离子增强化学气相沉积设备生长SiO2薄膜,以ZnO介质层作为Zn杂质诱导源,采用固态扩Zn的方式对激光器进行选择性区域诱导以制备非吸收窗口来提高器件的腔面光学灾变损伤阈值,从而提高半导体激光器的输出功率和长期可靠性。在580~680℃、20~60 min退火条件下对Zn杂质诱导量子阱混杂展开研究,实验发现,ZnO/SiO2或ZnO/Si3N4复合介质层的采用比单一Zn介质层的杂质诱导蓝移量大,且在680℃、30 min的条件下获得了最大55 nm的蓝移量。分析结果表明,介质层所施加的压应变会将外延片表面GaAs层中Ga原子析出,促使Zn原子进入外延层中以诱导量子阱混杂。通过测量光致发光光谱发现发光强度并没有明显下降,可为后期器件制作提供借鉴。

Highly spectra-stable pure blue perovskite light-emitting diodes based on copper and potassium co-doped quantum dots

Halide perovskite light emitting diodes(LEDs)have gained great progress in recent years.However,mixed-halide perovskites for blue LEDs usually suffer from electroluminescence(EL)spectra shift at a high applied voltage or current density,limiting their efficiency.In this work,we report a strategy of using single-layer perovskite quantum dots(QDs)film to tackle the electroluminescence spectra shift in pure-blue perovskite LEDs and improve the LED efficiency by co-doping copper and potassium in the mixed-halide perovskite QDs.As a result,we obtained pure-blue halide perovskite QD-LEDs with stable EL spectra centred at 469 nm even at a current density of 1,617 mA·cm^(−2).The optimal device presents a maximum external quantum efficiency(EQE)of 2.0%.The average maximum EQE and luminance of the LEDs are 1.49%and 393 cd·m^(−2),increasing 62%and 66%compared with the control LEDs.Our study provides an effective strategy for achieving spectra-stable and highly efficient pure-blue perovskite LEDs.

Preparation, Characterization and Photo-Catalytic Behavior of Y_2O_3/TiO_2 Composite Semiconductor Nanopowder

Y 2O 3/TiO 2 samples were prepared by sol-gel process and characterized by means of X-ray diffraction (XRD), laser Raman spectra (LRS), UV-visible diffuse reflectance spectra (DRS), specific surface area (BET), and transmission electron microscopy (TEM). The results show that the relative intensity of 101 peak of anatase and 002 peak of rutile, the mean crystal diameter and mean particle diameter of Y 2O 3/TiO 2 samples decrease while specific surface area increases owing to doping Y 2O 3. Y 2O 3/TiO 2 samples have a larger specific surface area and higher thermal stability. Owing to quantum size effect, the reflectance of Y 2O 3/TiO 2 samples is larger than that of pure TiO 2 in the range of 380～460 nm and the position of Raman peaks varies slightly. Being a model reaction, the photo-catalytic degradation of methylene blue (MB) with positive charge and methyl orange (MO) with negative charge was investigated in TiO 2 and Y 2O 3/TiO 2 nanopowder suspension irradiated by high-pressure mercury lamp. As a result, the addition of Y 2O 3 to TiO 2 is detrimental to photo-activity of TiO 2 for MB photo-degradation and photo-catalytic behavior is enhanced due to 5%, 10% Y 2O 3 deposited on TiO 2 for the photo-degradation of MO. And the relationship between photo-physical properties and photo-activity was discussed.

Polarized red, green, and blue light emitting diodes fabricated with identical device configuration using rubbed PEDOT:PSS as alignment layer

Polarized red, green, and blue light emitting diodes(LEDs) are successfully fabricated using polyfluorene and its derivatives, namely, poly(9,9-dioctylfluorene)(PFO), poly(9,9-dioctylfluorene-co-benzothiadiazole)(F8BT),and poly(triphenylamine-co-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole-co-benzo[c]thiadiazole-co-9,9-dioctyl-9 Hfluorene)(Red F).Rubbed hole transport layer poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate)(PEDOT:PSS)is employed in the devices as the alignment layer to achieve fully monodomain alignment in all polymer layers.Red F is blended with F8BT to realize the polarized electroluminescence of red light(dichroic ratio ~3.3), despite having no liquid crystallinity itself.Comparing PFO/F8BT blend to F8BT, higher efficiency of polarized emission is found due to the energy transfer.All the polarized LEDs exhibit pronounced dichroism and efficient polarized emission compared to the non-alignment regular devices.

多变量Si杂质诱导InGaAs/AlGaAs量子阱混杂研究

腔面光学灾变损伤是导致高功率量子阱半导体激光器阈值输出功率受限制的关键因素。通过量子阱混杂技术调整半导体激光器腔面局部区域处有源区材料的带隙宽度,形成对输出光透明的非吸收窗口,可提高激光器输出功率。本文基于InGaAs/AlGaAs高功率量子阱半导体激光器初级外延片,以外延Si单晶层作为扩散源,结合快速热退火方法开展了杂质诱导量子阱混杂研究。探索了介质层生长温度、介质层厚度、热处理温度、热处理时间等条件对混杂效果的影响。结果表明,50 nm的650℃低温外延Si介质层并结合875℃/90 s快速热退火处理可在保证光致发光谱的同时获得约57 nm的波长蓝移量。能谱测试发现,Si杂质扩散到初级外延片上的波导层是导致量子阱混杂效果显著的关键。

高功率蓝光半导体激光器巴条的封装技术研究

为实现高功率的蓝光半导体激光输出,对蓝光巴条的封装技术进行了研究。利用金锡硬焊料封装了高功率氮化镓(GaN)蓝光半导体激光巴条,应用铜钨过渡热沉作为缓冲层抑制了铜热沉和GaN激光芯片之间封装残余应力,采用高精度贴片机将芯片共晶键合在铜钨过渡热沉上。贴片质量的好坏直接影响了器件的输出特性,所以重点分析了贴片机的焊接温度焊接压力、焊接时间对器件的影响。实验结果表明:当贴片机的焊接温度为320℃、焊接压力为0.5 N、焊接时间为40 s时,焊料层界面空洞最少,热阻最低为0.565℃/W,阈值电流最低为4.9 A,在注入电流30 A时,输出光功率最高为32.21 W,最高光电转换效率达到了23.3%。因此,在优化焊接温度、焊接压力、焊接时间后,利用金锡硬焊料将蓝光半导体激光芯片共晶键合在铜钨过渡热沉的技术方案是实现蓝光半导体激光巴条高功率工作的有效途径。

Recent advances and prospects toward blue perovskite materials and light-emitting diodes

Perovskite based light-emitting diodes(PeLEDs)have become a powerful candidate for next-generation solid-state lightings and high-definition displays due to their high photoluminescence quantum yield(PLQY),tunable emission wavelength over the visible spectrum,and narrow emission linewidths.Over the past few years,the development of red-and green-emissive PeLEDs has rapidly increased,and the corresponding external quantum efficiencies(EQE)have exceeded 20%.However,the research progress of blue-emitting PeLEDs is limited by its poor material quality and inappropriate device structure.Currently,the maximum EQE of blue PeLED is only 6.2%,which is far from the industrialization requirements.In order to promote the development of blue PeLEDs,we summarize the recent research progress of blue perovskite materials and LEDs and discuss several fatal challenges,mainly embodied in low efficiency and poor stability.In order to overcome these challenges,detailed analysis and strategies are put forward in terms of the materials and devices.For the former,we summarize the feasible strategy for the preparation of efficient and stable blue-emissive perovskites using component engineering.For the latter,we analyze the advantages and limitations of the different strategies for blue-emissive perovskite in LEDs.At the end of the review,a comprehensive outlook is detailed,including future development directions and several technical problems to be solved.Thus,we aim to highlight the significance and promote the industrialization of PeLEDs.

Effect of Chloride Ion Concentrations on Luminescence Peak Blue Shift of Light-Emitting Diode Using Anti-Solvent Extraction of Quasi-Two-Dimensional Perovskite

In recent years,Perovskite Light-Emitting Diodes(PeLEDs)have received considerable attention in academia.However,with the development of PeLEDs,commercial applications of full-color PeLED technology are largely limited by the progress of blue-emitting devices,due to the uncontrollably accurate composition,unstable properties,and low luminance.In this article,we add Cesium chloride(CsCl)to the quasi-two-dimensional(quasi-2D)perovskite precursor solution and achieve the relatively blue shifts of PeLED emission peak by introducing chloride ions for photoluminescence(PL)and electroluminescence(EL).We also found that the introduction of chlorine ions can make quasi-2D perovskite films thinner with smoother surface of 0.408 nm.It is interesting that the EL peaks and intensities of PeLED are adjustable under different driving voltages in high concentration chlorine-added perovskite devices,and different processes of photo-excited,photo-quenched,and photo-excited occur sequentially with the increasing driving voltage.Our work provides a path for demonstrating full-color screens in the future.

A sensitization strategy for highly efficient blue fluorescent organic light-emitting diodes

Highly efcient blue fuorescent materials have recently attracted great interest for organic light-emitting diode(OLED)application.Here,two new pyrene based organic molecules consisting of a highly rigid skeleton,namely SPy and DPy,are developed.These two blue light emitters exhibit excellent thermal stability.The experiment reveals that the full-width at half-maximum(FWHM)of the emission spectrum can be tuned by introducing diferent amounts of 9,9-diphenyl-N-phenyl9H-fuoren-2-amine on pyrene units.The FWHM of the emission spectrum is only 37 nm in diluted toluene solution for DPy.Furthermore,highly efcient blue OLEDs are obtained by thermally activated delayed fuorescence(TADF)sensitization strategy.The blue fuorescent OLEDs utilizing DPy as emitters achieve a maximum external quantum efciency(EQE)of 10.4%with the electroluminescence(EL)peak/FWHM of 480 nm/49 nm.Particularly,the EQE of DPy-based device is boosted from 2.6%in non-doped device to 10.4%in DMAc-DPS TADF sensitized fuorescence(TSF)device,which is a 400%enhancement.Therefore,this work demonstrates that the TSF strategy is promising for highly efcient fuorescent OLEDs application in wide-color-gamut display feld.

Quantum-dot and organic hybrid light-emitting diodes employing a blue common layer for simple fabrication of full-color displays

Colloidal quantum-dot(QD)light-emitting diodes(QLEDs)have been in the forefront of future display devices due to their outstanding optoelectronic properties.However,a complicated solution-process for patterning the red,green,and blue QDs deteriorates the QLED performance and limits the resolution of full-color displays.Herein,we report a novel concept of QD–organic hybrid light-emitting diodes by introducing an organic blue common layer(BCL)which is deposited through a common mask over the entire sub-pixels.Benefitted from the optimized device structure,red and green QLEDs retained their color coordinates despite the presence of the BCL.Furthermore,adopting the BCL improved the external quantum efficiency of green and red QLEDs by 38.4%and 11.7%,respectively,due to the Förster resonance energy transfer from the BCL to the adjacent QD layers.With the BCL structure,we could simply demonstrate a full-color QD-organic hybrid device in a single substrate.We believe that this device architecture is practically applicable for easier fabrication of solution-processed,highresolution,and full-color displays with reduced process steps.

Structural Controls of Tetraphenylbenzene-based AIEgens for Non-doped Deep Blue Organic Light-emitting Diodes

Aggregation-induced emission(AIE)has emerged as a new concept,giving highly efficient solid-state photoluminescence.Particularly,AIE luminogens(AIEgens)with deep blue emission(400–450 nm)have displayed salient advantages for non-doped organic light-emitting diodes(OLEDs).However,deep blue emitters with Commission Internationale de L’Eclairage(CIE)coordinates less than 0.08 are still rare.In this review,we outline the latest achievements in the molecular guidelines based on the AIE core of tetraphenylbenzene(TPB)for developing efficient deep blue AIEgens.We provide insights into the construction of deep blue emitters with high horizontal orientation by regulating the length of the linear molecule.We also discuss the luminescence mechanisms of these AIEgens-based OLEDs by using the magnetic field effects measurements.Finally,a summary of the challenges and perspectives of deep blue AIEgens for non-doped OLEDs is also presented.

The Leap from Organic Light-Emitting Diodes to Organic Semiconductor Laser Diodes

In recent years,organic light-emitting device technology has expanded from organic light-emitting diodes(OLEDs)to organic semiconductor laser diodes(OSLDs)with the progress of sophisticated molecular and device architectural designs.In OLEDs,the development of thermally activated delayed fluorescence molecules has been intensively investigated recently.As a result,the internal quantum efficiency of OLEDs containing relatively simple aromatic compounds without precious metals has reached almost 100%.Furthermore,incorporating a distributed feedback resonator structure into the OLED architecture has yielded OSLDs that exhibit the features of current-pumped lasing.In this short review,the authors describe the recent paradigm shift from OLEDs to OSLDs,mainly fromthe perspective of materials innovation.

WO_3/TiO_2纳米材料的制备及光催化性能

采用溶胶-凝胶法制备 WO3/TiO2复合纳米光催化剂 .掺入 WO3、 TiO2锐钛矿 101峰的相对强度、平均晶粒直径与颗粒直径均减小，比表面积增大； WO3掺入摩尔比分别为 2％、 5％、 8％时，新的 LRS峰位分别出现在 797、 967及 969 cm－ 1;在 380－ 460 nm范围内， WO3/TiO2的反射率减小 .XPS分析表明， WO3/TiO2晶体中存在 W6＋、 W5＋、 W4＋和 Ti4＋、 Ti3＋ .以亚甲基蓝的光催化降解为反应模型，掺入 WO3后，光催化活性增强，掺入摩尔比为 2％时， WO3/TiO2的光催化活性最高 .还讨论了光催化活性与性质的关系 .

纳米复合Sb_2O_3/TiO_2的光催化性能研究

采用溶胶-凝胶法制备复合纳米 Sb2O3/TiO2。 Sb2O3掺入浓度越大，催化剂中锐钛矿相含量越高，晶粒直径与颗粒直径越小，比表面积越大。在 380～ 460nm范围内， Sb2O3/TiO2的反射率则减弱，表明光吸收增强。 XPS分析表明：掺入 2％ Sb2O3，出现新的 Ti2p3/2峰，对应于 Ti3＋，占 9.13％；锑以 Sb3＋、 Sb5＋两种形式存在， Sb5＋占 84.42％、 Sb3＋占 17.58％。以亚甲基蓝溶液光催化降解为模型反应，掺入 2％、 5％ Sb2O3，亚甲基蓝溶液的光催化脱色降解一级动力学常数与总有机炭（ TOC）去除率增大。发射光谱证明： Sb2O3的最佳比例为 2％，当其比例大于 2％时，其电子空穴对的复合率升高，光催化活性下降。

WO_3/TiO_2复合半导体的光催化性能研究

采用Ｓｏｌ－Ｇｅｌ法制备ＷＯ３／ＴｉＯ２纳米粉末．以高压汞灯为光源，亚甲基蓝溶液的光催化降解为模型反应．结果表明：掺入ＷＯ３摩尔比为２％时，ＷＯ３／ＴｉＯ２的光活性最高；随着热处理温度升高，ＷＯ３／ＴｉＯ２光活性增强；ＷＯ３／ＴｉＯ２的Ｌａｎｇｍｕｉｒ动力学常数为０．０１０３６ｍｍｏｌ／（Ｌ·ｍｉｎ）－１；紫外－可见吸收光谱及离子色谱分析结果表明：与ＴｉＯ２相比。

纳米复合Y_2O_3/TiO_2的制备、表征及其光催化性能研究

采用溶胶 凝胶法制备复合半导体Y2 O3/TiO2 。掺入Y2 O3会阻碍锐钛矿晶相的出现 ,掺入浓度越大 ,TiO2 锐钛矿 (10 1)峰强度减小越大、平均晶粒直径与颗粒直径减小、比表面积增大 ;Y2 O3/TiO2 具有高热稳定性与高比表面积 ,由于量子尺寸效应 ,掺入Y2 O3使光催化剂的拉曼峰发生微小位移 ,在 3 80～ 460nm范围内 ,使反射率增强。以亚甲基蓝与甲基橙溶液光催化降解为模型反应 ,掺入Y2 O3,复合光催化剂对亚甲基蓝溶液的光催化脱色降解一级动力学常数明显低于纯TiO2 的 ;掺入 5 %和 10 %Y2 O3,复合光催化剂对甲基橙溶液的光催化脱色降解一级动力学均常数高于纯TiO2 的 ,掺入浓度太高反而有害。讨论了掺入Y2