Flexible perovskite light-emitting diodes for display applications and beyond

The flexible perovskite light-emitting diodes(FPeLEDs),which can be expediently integrated to portable and wearable devices,have shown great potential in various applications.The FPeLEDs inherit the unique optical properties of metal halide perovskites,such as tunable bandgap,narrow emission linewidth,high photoluminescence quantum yield,and particularly,the soft nature of lattice.At present,substantial efforts have been made for FPeLEDs with encouraging external quantum efficiency(EQE)of 24.5%.Herein,we summarize the recent progress in FPeLEDs,focusing on the strategy developed for perovskite emission layers and flexible electrodes to facilitate the optoelectrical and mechanical performance.In addition,we present relevant applications of FPeLEDs in displays and beyond.Finally,perspective toward the future development and applications of flexible PeLEDs are also discussed.

Platinum complexes as phosphorescent emitters in highly efficient organic light-emitting diodes

Applications of platinum complexes as phosphorescent emitters in high efficiency organic light-emitting diodes （OLEDs） were shortly discussed in this paper. Key recent studies on highly efficient blue, green, red and white-phosphorescent OLEDs based on Pt complexes are presented in terms of efficiency and color quality.

Recent Advances in Patterning Strategies for Full‑Color Perovskite Light‑Emitting Diodes

Metal halide perovskites have emerged as promising light-emitting materials for next-generation displays owing to their remarkable material characteristics including broad color tunability,pure color emission with remarkably narrow bandwidths,high quantum yield,and solution processability.Despite recent advances have pushed the luminance efficiency of monochromic perovskite light-emitting diodes(PeLEDs)to their theoretical limits,their current fabrication using the spincoating process poses limitations for fabrication of full-color displays.To integrate PeLEDs into full-color display panels,it is crucial to pattern red–green–blue(RGB)perovskite pixels,while mitigating issues such as cross-contamination and reductions in luminous efficiency.Herein,we present state-of-the-art patterning technologies for the development of full-color PeLEDs.First,we highlight recent advances in the development of efficient PeLEDs.Second,we discuss various patterning techniques of MPHs(i.e.,photolithography,inkjet printing,electron beam lithography and laserassisted lithography,electrohydrodynamic jet printing,thermal evaporation,and transfer printing)for fabrication of RGB pixelated displays.These patterning techniques can be classified into two distinct approaches:in situ crystallization patterning using perovskite precursors and patterning of colloidal perovskite nanocrystals.This review highlights advancements and limitations in patterning techniques for PeLEDs,paving the way for integrating PeLEDs into full-color panels.

Perovskite light-emitting diodes toward commercial full-colour displays:progress and key technical obstacles

Metal-halide perovskite light-emitting diodes(PeLEDs)possess wide colour gamut,high luminescence efficiency,and low-cost synthesis,making them a promising photonic source for next-generation display applications.Since the first room-temperature emission PeLED was demonstrated in 2014,their performance has improved rapidly within a few years,leading to considerable attention from academia and industry.In this review,we discuss the primary technical bottlenecks of PeLEDs for commercial display applications,including large-area PeLED preparation,patterning strategies,and flexible PeLED devices.We review the technical approaches for achieving these targets and highlight the current challenges while providing an outlook for these perovskite materials and PeLED devices to meet the requirements of the next-generation high-colour-purity full-colour display market.

Design of LED display based on FPGA

If single chip micro computer controls light-emitting diode(LED),it needs abundant peripheral resources,but in this way,it is not convenient to be expanded,modified and maintained.In order to overcome these shortcomings,field programmable gate array(FPGA)is used to control LED.The hardware design uses low power consumption and high performance device EP1C6Q240C8.Quartus II is the software development environment.There are three modules built under the software development environment:divided clock module,word stock module and LED dot matrix display module,and these independent modules are connected to be a whole system.Finally,32×64 dot matrix display is realized successfully.It is convenient for the customer to adjust the three independent modules according to actual demands and it is easier to realize online updation.

ITO-free silicon-integrated perovskite electrochemical cell for light-emission and light-detection

Halide perovskite light-emitting electrochemical cells are a novel type of the perovskite optoelectronic devices that differs from the perovskite light-emitting diodes by a simple monolayered architecture.Here,we develop a perovskite electrochemical cell both for light emission and detection,where the active layer consists of a composite material made of halide perovskite microcrystals,polymer support matrix,and added mobile ions.The perovskite electrochemical cell of CsPbBr3:PEO:LiTFSI composition,emitting light at the wavelength of 523 nm,yields the luminance more than 7000 cd/m2 and electroluminescence efficiency of 4.3 lm/W.The device fabricated on a silicon substrate with transparent single-walled carbon nanotube film as a top contact exhibits 40%lower Joule heating compared to the perovskite optoelectronic devices fabricated on conventional ITO/glass substrates.Moreover,the device operates as a photodetector with a sensitivity up to 0.75 A/W,specific detectivity of 8.56×1011 Jones,and linear dynamic range of 48 dB.The technological potential of such a device is proven by demonstration of 24-pixel indicator display as well as by successful device miniaturization by creation of electroluminescent images with the smallest features less than 50μm.

Liquid crystal display and organic light-emitting diode display: present status and future perspectives

Recently,‘Liquid crystal display(LCD)vs.organic light-emitting diode(OLED)display:who wins?’has become a topic of heated debate.In this review,we perform a systematic and comparative study of these two flat panel display technologies.First,we review recent advances in LCDs and OLEDs,including material development,device configuration and system integration.Next we analyze and compare their performances by six key display metrics:response time,contrast ratio,color gamut,lifetime,power efficiency,and panel flexibility.In this section,we focus on two key parameters:motion picture response time(MPRT)and ambient contrast ratio(ACR),which dramatically affect image quality in practical application scenarios.MPRT determines the image blur of a moving picture,and ACR governs the perceived image contrast under ambient lighting conditions.It is intriguing that LCD can achieve comparable or even slightly better MPRT and ACR than OLED,although its response time and contrast ratio are generally perceived to be much inferior to those of OLED.Finally,three future trends are highlighted,including high dynamic range,virtual reality/augmented reality and smart displays with versatile functions.

The fabrication of color-tunable organic light-emitting diode displays via solution processing

Electroluminescent devices based on organic semiconductors have attracted significant attention owing to their promising applications in flat-panel displays.The conventional display pixel consisting of side-by-side arrayed red,green and blue subpixels represents the mature technology but bears an intrinsic deficiency of a low pixel density.Constructing an individual color-tunable pixel that comprises vertically stacked subpixels is considered an advanced technology.Although color-tunable organic light-emitting diodes(OLEDs)have been fabricated using the vacuum deposition of small molecules,the solution processing of conjugated polymers would enable a much simpler and inexpensive manufacturing process.Here we present the all-solution processing of color-tunable OLEDs comprising two vertically stacked polymer emitters.A thin layer of highly conducting and transparent silver nanowires is introduced as the intermediate charge injection contact,which allows the emission spectrum and intensity of the tandem devices to be seamlessly manipulated.To demonstrate a viable application of this technology,a 4-by-4 pixelated matrix color-tunable display was fabricated.

Emissive displays with transfer-printed assemblies of 8 μm × 15 μm inorganic light-emitting diodes

Displays using direct light emission from microscale inorganic light-emitting diodes(μILEDs)have the potential to be very bright and also very power efficient.High-throughput technologies that accurately and cost-effectively assemble microscale devices on display substrates with high yield are key enablers forμILED displays.Elastomer stamp transfer printing is such a candidate assembly technology.A variety ofμILED displays have been designed and fabricated by transfer printing,including passive-matrix and active-matrix displays on glass and plastic substrates.

Design of compensation pixel circuit with In-Zn-O thin film transistor for active-matrix organic light-emitting diode 3D display

This paper presents a new compensation pixe] circuit suitable for active-matrix organic light-emitting diode （AMOLED） stereoscopic three dimensional （3D~ displays with shutter glasses. The simultaneous emissio~ method was used to solve the crosstalk problem, in which the periods of initialization and threshold voltage detectio11 occur for each pixel of whole panel simultaneously. Furthermore, there was no need of the periods of initialization and threshold voltage detection from the second frame beginning by one-time detection method. employing threshold voltage The non-uniformity of the proposed pixel circuit was considerably low with an average value of 8.6% measured from 20 discrete proposed pixel circuits integrated by In-Zn-O thin film transistors （IZO TFTs）. It was shown that the OLED current almost remains constant for the number of frames up to 70 even the threshold voltage detection period only exists in the first frame.

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.

柔性显示器

本文介绍了柔性显示器的特点、应用和技术发展现况，并简述了它的发展前景。

Flexible organic light-emitting diodes with poly-3,4-ethylene-dioxythiophene as transparent anode

The flexible oragnic light-emitting diodes (OLEDs) fabricated on poly -3,4-ethylenedioxythiophene/poly -styrenesulfonate(PEDOT/PSS) coated substrates were demonstrated. How the fabricating processes and the device structure will affect the device performance was studied and the atomic force microscopy was employed to analyze the mophorlogy of the conducting polymer anode. Under optimized conditions, flexible OLEDs with PEDOT anode showed the brightness up to 2760 cd/m2 and maximum external quantum efficiency of 1.4%. These data are comparable to those of conventional flexible OLEDs with ITO anode.

Device performance and light characteristics stability of quantum-dot-based white-light-emitting diodes

Advances in image quality in recent decades have made it necessary to develop new technologies for producing displays to meet remarkably stricter standards. The display market is governed mainly by liquid crystal display and light-emitting diode （LED） technology; however, it suffers from limitations that can be overcome by developing the next generation of electroluminescent displays. The introduction of colloidal quantum dots （QDs） as down-converters has enabled the production of displays with extremely high color purity and gamut. Therefore, colloidal nanocrystals are excellent candidates for the preparation of electroluminescent devices, which represent a straightforward approach to the development of unprecedented high-quality displays. We synthesized light-emitting QDs covering the entire visible spectrum with high fluorescence quantum yields and color purity, and produced high-brightness single-color LEDs with external quantum efficiencies of 0.39%, 1.04%, 2.10%, and 1.30% for red-, orange-, green-, and blue-emitting dots, respectively. Additional136 white LEDs were prepared by mixing QDs; they showed color temperatures of 5,300 K and color rendering indices exceeding 80%. Very importantly, we exhaustively characterized the LED performance, including the response time, stability, and evolution of the light characteristics, thus providing crucial information toward the development of high-quality electroluminescent displays.

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.

Pure RGB Emissions Based on a White OLED Combined with Optical Colour Filters

We report on a white organic light emitting device （OLED） with a single light emitting layer consisting of a greenish-white emitting host bis-（2-（2-hydroxyphenyl） benzothiazole）zinc （Zn（BTZ）2 ） and an orange-red dopant 5,6,11,12-tetraphenylnaphthacene （rubrene）. The Commission Internationale De L＇Eclairage （CIE） coordinates, external quantum efficiency, and brightness of the white OLED are （0.341, 0.334）, 0.63% and 4000 Cd/m^2 at the bias of 20 V, respectively. Pure red-green-blue （RGB） emissions have been successfully achieved from the white OLED combined well with several built-in optical colour filters （CFs）. The CIE coordinates of the white mixture calculated in theory are very close to the coordinates of the white mixture which recorded with spectrophotometer in practice.

Design on general development platform for FPD systems

In this paper, a multi-functional development platform for flat panel display （FPD） development is proposed. With the proposed development platforms, a variety of FPD devices, including organic light-emitting diode （OLED） screens, liquid crystal display （LCD） screens with touchscreens, OLED microdisplay screens, etc., can be directly and instantly connected, examined and utilized. A field-programmable gate array （FPGA） is used in the development system to drive different types of FPD devices, and ARM11S3C6410 is used as the application processor to provide various services. The development system uses Linux as the system kernel, Qt for Embedded Linux as the UI framework, various system libraries for video and audio services, and a custom-made user engine for fine-polished appearance and behavior. The development platform has been used not only in testing and verification of the FPD devices, but also in building OLED-powered handheld digital devices, shortening the development cycle from OLED devices to mature application products.

Seeking new,ultra-narrow-band blue emitting phosphors with high color purity for wide color gamut displays

Ultra-narrow-band phosphors have gained widespread applications in lighting and displays to enhance brightness and improve color saturation.Typical phosphor designs employ UCr_(4)C_(4)-type compounds and designing new narrow-band phosphors with high color purity is a major challenge.Here,we explored a Eu^(2+)-doped Ba_(5)GeO_(4)Br_(6)phosphor,showing a narrow-band blue emission(λ_(em)=436 nm) excitation at the near-ultraviolet light with a full width at half maximum of 30.7 nm and high color purity of 96.6%.In addition,attractive cathodoluminescence characteristics were systematically analyzed by varying filament current(30-70 mA) and accelerating voltage(3-7 eV).Robust anti-degradation behavior and color point stability under continuous electron beam bombardment were confirmed.Given its excellent performance in photoluminescence and cathodoluminescence,application in wide color gamut displays appears promising.Using commercial phosphors β-SiAlON:Eu^(2+)and K_(2)SiF6:Mn^(4+)as green and red light co nverte rs respectively,and the title phosphor as the blue light converters,the fabricated w-LED exhibits a wide color gamut of 82% NTSC.