Display Applications Research Articles

Inkjet‐printed quantum dot light‐emitting diodes: Development and challenges for display applications

AbstractQuantum dot (QD) technology is rapidly advancing and draws much attention for display applications where accurate and vibrant color reproduction is highly required. Currently, significant research is being conducted in developing quantum dot light‐emitting diode (QD‐LED) as next‐generation displays. QD‐LEDs offer several advantages, including high color purity, wide color gamut, and lower manufacturing costs. Recent advancements in QD synthesis and device engineering have significantly improved the performance of QD‐LEDs, but several challenges must be addressed for the successful commercialization. In this article, we provide an overview of QD‐LED developments and key issues that are required to be solved for realizing practical inkjet‐printed QD‐LED displays.

Performance improvement of red, green and blue InGaN micro-LEDs with distributed Bragg reflector

Abstract Red-green-blue (RGB) micro light-emitting diodes (micro-LEDs) without distributed Bragg reflector (DBR), with air-separating DBR, and with integrated DBR, were demonstrated. The effect of the DBRs as reflectors on the external quantum efficiency (EQE) and electroluminescence (EL) spectra enhancement of RGB micro-LEDs was systematically investigated for realizing higher-performance micro-LEDs for display applications. At 5 A/cm2, the EQEs of the RGB micro-LEDs with integrated DBR were improved by 38%, 33%, and 32%, respectively, with comparison to the RGB DBR free micro-LEDs. Further, the full width at half maximum (FWHM) of the red micro-LEDs was reduced by 4.3 nm at 50 A/cm2 with the integrated DBR due to the higher enhancement of the central wavelength spectrum. The green and blue micro-LEDs with integrated DBR had higher EQE and the red micro-LEDs with integrated DBR had narrower FWHM compared to those with air-separating DBR. However, the peak wavelength of the RGB micro-LEDs with integrated DBR shifted, resulting in a lower color gamut in CIE 1931. The above work provides guidance for future full-color micro-display applications based on RGB InGaN micro-LED technology.

Internal quantum efficiency improvement of InGaN-based red LED by using double V-pits layers as strain relief layer

Micro/mini light emitting diodes (LEDs) based on AlInGaN material system have vast potential in display applications. Nevertheless, the low internal quantum efficiency (IQE) of InGaN-based red LED limits its development and application. In the epitaxial structure of our designed red LED, double V-pits layers were used as strain relief layers to reduce compressive strain and improve the IQE of the active layer. First, InGaN/GaN superlattices (SLs) were grown below the active layer to form low-density large V-pits layer. Subsequently, multi-period green and red composite quantum wells were adopted as the active layer. A high-density small V-pits layer was introduced into the active region to release the compressive strain by adjusting the growth parameters of green multiple quantum wells (MQWs). The V-shaped pits divide the continuous large-area of active layer into mutually isolated small pieces, which prevents the transmission of strain and converts the long-range strain into separated local strain. The peak IQEs of LED A2 with single V-pits layer and LED B4 with double V-pits layers were measured to be 10.5% at 613 nm and 21.5% at 612.1 nm, respectively. The IQE is greatly improved by 204.7%. The research results indicate that the double V-pits layers structure can alleviate the compressive strain of InGaN QWs more effectively, reduce the influence of piezoelectric polarization field, and improve the IQE.

ZnO nanowire broadband ultra-wide-angle optical diffusers grown by aqueous chemical bath deposition

Light traveling path management is one of the key technologies to improve the performance of lighting, displays, and solar cells. Here we report broadband ultra-wide-angle optical diffusers using ZnO nanowires grown on flexible substrates by aqueous chemical bath deposition. The growth behavior of ZnO nanostructures strongly influences the degree of light scattering and is mainly governed by the molecular complexes present in the chemical bath, their relative concentration, and their interactions, which were efficiently controlled by the ammonia concentration in this work. Our ZnO nanowires grown at optimal ammonia concentrations exhibit higher optical transmission haze values than previously reported ZnO nanostructures over broadband (400 – 800 nm). In addition, our ZnO nanowires exhibit larger values in the key parameters of total transmittance and light scattering angle than commercial 3 M™ optical diffusers 3635–30/3635–70. Therefore, our chemical bath deposited ZnO nanowires are expected to be a compelling solution for optical diffusers in display and lighting applications.

Ultrabroadband chromaticity-programmable random lasing based on waveguide-assisted pumping strategy

Chromaticity-tunable random lasers (RLs) have wide applications in laser display and imaging. However, the achievable chromaticity range poses challenges due to their inherent randomness and the inevitable loss. Here, an ultrabroadband chromaticity-programmable RL has been demonstrated via waveguide-assisted pumping strategy. The unique configuration with destroyed waveguide supplies an excellent platform for achieving full color random lasing through the cascade pumping process. Random lasing with tunable wavelengths spanning the entire visible range is achieved via side-pumping schemes. The eight acceptor RLs can be simultaneously pumped to obtain chromaticity-programmable random lasing, showcasing a Commission Internationale de l'Eclairage (CIE) color map with 155% more perceptible colors than the standard red-green-blue space. This opens the possibilities for programmable RLs with potential applications in biological imaging and smart sensing.

Improving bias stability of IGZO field-effect transistors through CF4 plasma treatment of Al2O3 dielectrics

In this study, the effects of the CF4 plasma treatment on the amorphous indium gallium zinc oxide (IGZO) material were explored. The electrical characteristics of the IGZO-based field-effect transistor (FET) were also thoroughly examined to analyze the influence of the plasma treatment. Excellent adhesion of the sol-gel-based IGZO semiconducting film was achieved owing to the strong dipole moment of the AlOxFy layer created by the surface treatment. In particular, X-ray photoelectron spectroscopy depth profiles and transmission electron microscopy electron energy loss spectroscopy analyses provided clear evidence that fluorine atoms diffused into the Al2O3 surface via the CF4 plasma treatment. The formation of an AlOxFy layer at the IGZO/Al2O3 interface is expected to be advantageous for reducing the interface trap density, thereby enhancing the critical transistor parameters. Additionally, the plasma-treated IGZO transistor demonstrated strong electrical bias stability under continuous gate bias stress conditions. Therefore, surface modification via CF4 plasma treatment is proposed to boost the stability and performance of the device, offering a straightforward approach for integrated thin-film transistor circuitry in advanced display applications.

Development of Low-interference, Resistance to Moisturethermal Adhesion Film for Display Applications

Development of Low-interference, Resistance to Moisturethermal Adhesion Film for Display Applications

Size and temperature effects on optoelectronic properties of Micro-LED arrays for display applications

In recent years, Micro-light-emitting diode (Micro-LED) has attracted much attention in the display field, because it provides the possibility of high pixel density, etc. The implementation of high pixel density is accompanied by the reduction of size, during which the performance degradation caused by sidewall defects gradually increases. At the same time, the increase in power density and difficulty in heat dissipation caused by high pixel density can also lead to poor thermal management, resulting in an increase in junction temperature, thus affecting the display effect. In this paper, we prepared seven different sizes of Micro-LED and studied the influence of size and temperature effects on the optoelectronic properties. Smaller-sized Micro-LED could withstand higher current densities because it was not affected by the current crowding effect. However, it tends to have a larger series resistance (RS) and a lower external quantum efficiency (EQE) due to sidewall defects created during etching. The luminance of the 100 μm and 7 μm Micro-LED was 340000 cd/m2 (at 83 A/cm2) and 32000 cd/m2 (at 773 A/cm2), respectively. The peak EQE of 100 μm Micro-LED was 16.87 %. On this basis, the temperature-dependence of the optoelectronic properties of 10 μm and 50 μm Micro-LED were studied. The larger the size of Micro-LED, the better the operational stability it exhibited. From the room temperature (RT) rose to 100 ℃, the EQE of the 10 μm and 50 μm Micro-LED decreased by 16 % and 13.1 %, respectively. These experimental results provide important data for the design and preparation of Micro-LED of different sizes and for exploring the operational stability at high temperatures.

Bio-inspired colloidal photonic crystal pattern with multiple optical variable images

Colloidal photonic crystals (CPCs) are highly significant for display and anti-counterfeiting applications due to their vibrant structural colors and light-manipulating properties. Efficient and extensive CPC patterns is required for practical applications. Additionally, it is essential to incorporate complex optical elements or responsive qualities to the CPC patterns in order to enhance their performances for security applications. Herein, we proposed CPC patterns with alterable images revealed by changes in viewing angle or exposure to certain vapors. The CPC patterns were prepared by inkjet printing method. Through substrate modification to achieve varying wettability, angle-dependent optical adaptable images could potentially be shown by the patterns. The mesoporous silica nanoparticles (MSNs) were employed as building blocks to impart vapor-chromic characteristics to the CPC patterns. The CPC complex patterns responsive optical characteristics rendered them suitable for use in public authentication and anti-counterfeiting applications.

Bright Structural-Phase-Pure CsPbI3 Core-PbSO4 Shell Nanoplatelets With Ultra-Narrow Emission Bandwidth of 77 meV at 630 nm.

Achieving a narrow emission bandwidth islong pursued for display applications. Among all primary colors, obtaining pure red emission with high visual perception is the most challenging. In this work, CsPbI3 halide perovskite nanoplatelets (NPLs) with rigorously controlled 2D [PbI6]4- octahedron layer number (n) are demonstrated. A perovskite core-PbSO4 shell structure is designed to prevent aggregation and fusion between NPLs, enabling consistent thickness and quantum confinement strength for each NPL. Consequently, exact n = 4 CsPbI3NPLs are demonstrated, exhibiting emission peaks around 630nm, with very narrow spectral bandwidths of <24nm and high absolute photoluminescence quantum yields up to 85%. The emission of n = 4 NPLs falls exactly within the pure-red region, closely aligning with the International Telecommunication Union Recommendation BT.2020 standard. Measurements suggest predominant stability and color homogeneity compared to traditional red-emitting CsPbIxBr3- x nanocrystals. Finally, proof-of-concept pure-red emissive light-emitting diodes (LEDs) are demonstrated by integrating n = 4 CsPbI3 NPLs films with a blue LED chip, showing an excellent external quantum efficiency of 18.3% and high brightness exceeding 3 × 106 nits. Stringent requirements for future display technologies, are satisfied based on the high color purity, stability, and brightness of CsPbI3 NPLs.

Pure-Phase Perovskite Quantum Well for Green Light-Emitting Diodes.

Perovskite multiple quantum wells (MQWs) have shown great potential in the field of light-emitting diodes (LEDs). However, the random formation of QWs with varying well widths (n numbers) often leads to suboptimal interface defects and charge transport issues. Here, we reveal that the crystallization sequence of bromide-based perovskite MQWs is large-n QWs preceding small-n QWs. With this insight, we prevent the crystallization of subsequent small-n QWs by reducing the crystallization rate, ultimately resulting in the crystallization of only n = 5 QWs. This reduction in the crystallization rate is achieved through the chemical interaction of dual additives with perovskite constituents. Additionally, the chemical interaction effectively passivates the uncoordinated lead ions defects. Consequently, pure-phase perovskite QWs with a high photoluminescence quantum efficiency of 75% are achieved. The resulting green LEDs achieve a peak external quantum efficiency of 17.1% and a maximum luminance of 29,480 cd m-2, which is attractive for full-color display applications of perovskites.

High efficiency in blue TADF OLED using favorable horizontal oriented host

An appropriate host featuring a wide band gap (Eg) and high triplet energy (T1) is crucial for facilitating highly efficient blue-light emitting devices. In this study, 4Ac26CzBz, a new host comprising acridan and carbazole moieties linked to a benzimidazole core, has been synthesized and characterized. Notedly, 4Ac26CzBz exhibits a wide optical gap (Eg) and high triplet energy (T1) of 3.3 and 3.0 eV, respectively, and has been proven a suitable host for blue thermally activated delayed fluorescence (TADF) OLED. By adopting 4TCzBN as a blue-light dopant, a remarkably high device external quantum efficiency of 35.8 % (59.8 cd/A and 62.8 lm/W) and a low turn-on voltage (<3 eV) have been demonstrated, with significant suppression of the efficiency roll-off, maintaining a high efficiency of 29.7 % as luminance at 1000 cd/m2. This excellent performance is deduced from the host’s ambipolar carrier transporting properties, which refer to its ability to transport both electrons and holes effectively, high photoluminescence quantum yield (PLQY) of 98.6 %, and highly horizontal orientation of transition dipole, as determined through diverse analytical measurements. The good material properties of 4Ac26CzBz and the high OLED performance reveal its potential for the next generation’s advanced display and lighting applications.

Enhanced horizontal alignment of InGaN/GaN nanorod LEDs via insulator-based dielectrophoresis

GaN-based nanorod light emitting diodes (LEDs) are key to the development of high brightness, small pixel size, and long lifetime for high-resolution display applications. To manufacture individual nanorod LEDs as compact light sources, it is necessary to separate the nanorod LEDs from the substrate and transfer them to the electrode. Dielectrophoresis (DEP) is a highly suitable technique for transferring the individual nanorod LEDs. However, there are still challenges in achieving a high alignment yield. In this work, nanorod LEDs are successfully fabricated and separated to enhance the horizontal alignment in interdigitated electrodes via insulator-based DEP (iDEP). In iDEP, a structure is formed by inserting an insulating layer between the electrodes. This structure manipulates the electric field generated around the electrodes due to polarization by the insulating layer. This results in a relatively uniform electric field distribution on the surface of the insulating layer, thereby enhancing the horizontal alignment of the nanorod LEDs. Herein, the iDEP structure achieves significant nanorod LED alignment yield of up to 91.9 %, compared to 45.5 % for the electrode-based DEP (eDEP) technique. Furthermore, the use of a patterned insulator makes it possible to restrict 1 or 2 aligned nanorod LEDs within a specific pixel region, which is suitable for high-resolution display technologies based on nanorod LEDs.

Comparative computational analysis of orthoconic antiferroelectric liquid crystals: DFT analysis.

The study undertakes a comparative analysis of four distinct semi-fluorinated chiral Organic Active Ferroelectric Liquid Crystals (OAFLCs). The comparative analysis of the compounds is done by using various parameters, including thermodynamic, non-linear optical, electrical, atomic charge distribution, and atomic orientations. We use optimization algorithms to look at chemical reactivity, electrical properties, intermolecular interactions, and static hyperpolarizability. Sample 4 is the best choice for a wide range of display applications. This research contributes to understanding the nuanced properties of semi-fluorinated chiral OAFLCs and highlights Sample 4's potential for novel applications in display technology, owing to its superior stability and optimized properties. This study helps to enhance our understanding of the comparative analysis of semi-fluorinated chiral OAFLCs for potential advancements in display technologies by incorporating findings from key studies. The simulations are performed using density functional theory (DFT) with the B3LYP functional for predicting molecular properties, and Vibrational Energy Distribution Analysis (VEDA) software is used to perform the vibrational analysis of the molecules.

Lensless phase-only holographic Maxwellian display based on double-phase decomposition for optical see-through near-eye display applications

The holographic Maxwellian display holds significant potential as a technique for augmented reality presentations due to its capability to address the vergence-accommodation conflict in see-through near-eye displays. However, conventional lensless holographic Maxwellian displays predominantly rely on amplitude-type holograms, facing challenges such as low diffraction efficiency and interference from conjugate images. To overcome these limitations, we propose a lensless phase-only holographic Maxwellian display tailored for optical see-through near-eye applications. In our approach, a complex amplitude distribution, calculated using the angular spectrum diffraction method, was encoded into a phase hologram via the double-phase decomposition algorithm. This phase hologram can effectively converge the virtual target image onto the viewer’s pupil by multiplying the phase hologram with a convergent spherical wave at the hologram plane, enabling viewers to consistently perceive all-in-focus images at the pupil location. Additionally, we introduced a digital grating to mitigate the interference caused by other-order diffraction images. Finally, experimental results demonstrated that our proposed near-eye display system can accurately generate see-through virtual images without the vergence-accommodation conflict issue by loading the designed phase hologram onto a phase-type spatial light modulator. Furthermore, the eye box expansion has been realized by multiplying the phase hologram with multiple convergent spherical waves.

Design of Compact Dielectric Metalens Visor for Augmented Reality Using Spin-Dependent Supercells

Augmented reality overlays computer-generated virtual information onto real-world scenes, enhancing user interaction and perception. However, traditional augmented reality optical systems are usually large, bulky, and have limited optical performance. In this paper, we propose a novel compact monochrome reflective dielectric metalens visor with see-through properties, engineered using a periodic structure of spin-dependent supercells. The supercell, which is composed of staggered twin nanofins, provides spin-dependent destructive or constructive interference with different circularly polarized incidences. The design combines the principles of interference with the Pancharatnam–Berry phase to enhance reflection at a working wavelength of 650 nm while maintaining good transmission. Right circularly polarized light incident from the substrate side causes destructive interference, enabling the supercell to work in reflection mode, while left circularly polarized light causes constructive interference, enabling the supercell to work in transmission mode. Furthermore, the supercell-constructed metalens can achieve near-diffraction-limited reflective focusing and a broad diagonal field of view of approximately 96°. In addition, compared to transmissive metalens visors, the reflective design eliminates the need for a beam splitter, significantly reducing the size and weight of the system. Our work could facilitate the development of compact and lightweight imaging systems and provide valuable insights for augmented reality near-eye display applications.

Manipulating exciton confinement for stable and efficient flexible quantum dot light-emitting diodes

Flexible quantum dot light-emitting diodes (QLEDs) show great promise for the next generation of flexible, wearable, and artificial intelligence display applications. However, the performance of flexible QLEDs still lags behind that of rigid substrate devices, hindering their commercialization for display applications. Here we report the superior performance of flexible QLEDs based on efficient red ZnCdSe/ZnS/ZnSe QDs (A-QDs) with anti-type-I nanostructures. We reveal that using ZnS as an intermediate shell can effectively confine the exciton wavefunction to the inner core, reducing the surface sensitivity of the QDs and maintaining its excellent emission properties. These flexible QLEDs exhibit a peak external quantum efficiency of 23.0% and a long lifetime of 63,050 h, respectively. The anti-type-I nanostructure of A-QDs in the device simultaneously suppresses defect-induced nonradiative recombination and balances carrier injection, achieving the most excellent performance of flexible QLEDs ever reported. This study provides new insights into achieving superior performance in flexible QD-based electroluminescent devices.

The role of sub-regional electrostatic spinning nanofiber loaded with WO3 nanoparticle in modulating electro-optic performance and stepwise display of polymer dispersed liquid crystal

ABSTRACT The advancement of multi-functional displays with outstanding electro-optical properties is particularly essential at present. However, conventional integral all-area driven transparent displays are gradually failing to meet current demands. Herein, sub-regional electrostatic spinning of nanofibers as a novel fabrication method was introduced into polymer-dispersed liquid crystal (PDLC) to achieve stepwise display in concert with loaded WO3 nanoparticles, addressing the aforementioned drawback. The use of nanofibers played a crucial role in ensuring fine dispersion of nanoparticles, resulting in a reduction of the saturation voltage of the PDLC film from 28.9 V to 19.7 V and an increase in contrast ratio from 105.7 to 194.3. Meanwhile, experimental findings and theoretical considerations have revealed that variations in microscopic pore size can significantly influence the electro-optical behaviour of PDLC film. Next, the stepwise PDLC film was prepared by electrostatically spinning nanofibers onto half of the LC cell region, leading to different voltage-transmittance responses between the two regions. Consequently, under appropriate driving voltages, the PDLC film can realise three different optical states: total scatter, half-transparency, and total transparency. In addition, the PDLC film exhibited excellent anti-thermal ageing performance, allowing it to excel in various advanced display applications.

Regulating ligand length to improve the PL QY and stability of CsPbCl0.9Br2.1 nanocrystals for LEDs and photoelectric applications

Perovskite luminescent materials have been extensively investigated due to their comprehensive applications for full-color display, lighting, and communication. However, the development of blue-emissive perovskites has seriously lagged behind that of green and red counterparts, primarily because of their low photoluminescence quantum yield (PL QY) and poor stability. Here, we prepared blue-emissive CsPbCl0.9Br2.1 perovskite nanocrystals (PeNCs) and enhanced their QY from 61.3 % to 90.4 % by regulating the chain lengths of ligands. Post-treated PeNCs also exhibit good stability, their PL intensity is maintained at about 90 % after storage at ambient conditions for 10 days. The exciton dynamics results obtained from time-resolved fluorescence spectra and transient absorption spectra show that dodecyldimethylammonium bromide (DDAB), featuring double 12-hydrocarbon chains, is more capable of passivating surface defects and inhibiting non-radiative composites than the other double 8- or double 16-carbon chain ligands, which greatly improved the probability and rate of radiative recombination. Subsequently, the mechanism of ligand chain length regulation on the PL properties and stability of PeNCs was analyzed in terms of ligand-NC surface interaction, ligand polarity, hydrophobicity, and spatial effects. Furthermore, the device based on DDAB-CsPbCl0.9Br2.1 demonstrated stable EL and long operation lifetime, indicating its significant potential as an efficient blue emitter for backlighting in display technologies.

Room-Temperature Persistent Phosphorescence of Aggregated Gold Nanoclusters under Molecular Crystal Confinements.

We report color-tunable and solvent-processable persistent fluorescence to phosphorescence switching at room temperature by doping gold nanoclusters (AuNCs) inside molecular crystals. This provides a significant insight into the tunability of the photoluminescence property of the dopant depending on the crystal environment and compactness of confinement, with the possibility of energy transfer from crystal to aggregated AuNCs. For test cases, we have doped histidine-stabilized AuNCs (HIS-AuNCs) inside histidine (HIS-AuNCs-HIS) and isophthalic acid (HIS-AuNCs-IPA) crystals, respectively, and glutathione-stabilized AuNCs (GSH-AuNCs) inside histidine crystals (GSH-AuNCs-HIS). The maximal phosphorescence decay time recorded for crystal doped aggregated AuNCs was 9.38 ms, and the photoluminescence quantum yield value was measured as 25%. The possible energy states and potential interactions between aggregated NCs and host crystals were accounted for through density functional theory calculations and docking techniques, respectively. This finding opens new possibilities for designing and producing color-tunable persistent AuNC-based luminous crystals for multilayer information encryption, display, and biological applications.