High Color Gamut Research Articles

Optimization study on circadian tunability and Rec. 2020 of RGB-LED-based displays considering the users with different ages

The reasonable design of spectral power distribution (SPD) of GaN-based light-emitting diode (LED) display becomes more and more important and popular. In this work, we perform an investigation on the circadian effects of three-primary (red R, green G, and blue B, also denoted as RGB) LED based self-luminous displays (such as emerging mini-LED or micro-LED based displays) considering the users with different ages. With the increment of peoples’ ages from 1 year to 100 years, the optical transmittance of humans’ eyes may decrease due to the aging of their body functions. Therefore, it is important and meaningful for performing a spectral optimization study on the circadian effects of light that is emitting from self-luminous LED-based displays for the users with different ages. Here, the melanopic efficacy of luminous radiation (MELR) is mainly used to evaluate the circadian effects of white light coming from RGB-LED displays. With the aid of multi-objective optimization genetic algorithm (MOGA), the maximum MELR and the minimum MELR value are separately obtained for the standard observers at the age of 32, while maintaining at a certain high color gamut of Rec. 2020 standard (i.e., 60 %, 70 %, 80 %, and 90 % Rec. 2020, respectively) for these LED-based displays. Then, an extrapolation of optimal SPD at the age of 32 is done to other ages. Another parameter that can be denoted as circadian stimulus (CS) is also calculated and discussed for different ages. It is believable that this work is helpful for guiding the design and fabrication of future RGB-LED-based displays in consideration of the users with different ages, meeting large requirements of human-centric lighting (HCL) in the future.

Reconfigurable and polarization-dependent optical filtering for transflective full-color generation utilizing low-loss phase-change materials

All-dielectric metasurface, which features low optical absorptance and high resolution, is becoming a promising candidate for full-color generation. However, the optical response of current metamaterials is fixed and lacks active tuning. In this work, we demonstrate a reconfigurable and polarization-dependent active color generation technique by incorporating low-loss phase change materials (PCMs) and CaF2 all-dielectric substrate. Based on the strong Mie resonance effect and low optical absorption structure, a transflective, full-color with high color purity and gamut value is achieved. The spectrum can be dynamically manipulated by changing either the polarization of incident light or the PCM state. High transmittance and reflectance can be simultaneously achieved by using low-loss PCMs and substrate. The novel active metasurfaces can bring new inspiration in the areas of optical encryption, anti-counterfeiting, and display technologies.

77‐3: Power‐Efficient and High‐Color‐Gamut RGBY AMOLED Displays

We present a novel four color sub‐pixel active matrix organic light emitting Device (AMOLED) display that uses only three OLED depositions while enabling very high color gamut with greatly reduced power consumption. Achieving 90% of Rec. 2020 color standard, power consumption is reduced by 39% compared to that of a conventional RGB side‐by‐side top emission (TE) pixel architecture.

49‐3: Invited Paper: High‐Resolution Color‐Reflective Bistable Cholesteric Liquid Crystal Technology for Signage Applications

An optimized color‐reflective LCD with high optical performances and cost‐effective structure has been proposed by association with cholesteric liquid crystal technology. By way of a color dithering algorithm, the cholesteric liquid crystal display (Ch‐LCD) can visualize a 24‐bit RGB color pixel and display over 16 million colors. Moreover, the waveform module (WF) is applied to emulate the display timing controller, which is a lowcost and more accessible way to drive the Ch‐LCD. In this paper, we demonstrated a 13.3‐inch passive matrix (PM) driven Ch‐LCD with a high resolution of 202 PPI, high reflectance of 30%, and high color gamut of 20%, which is suitable for electronic signage applications.

Efficient OLEDs with Alleviated Efficiency Roll‐Off Based on MR‐TADF Materials Containing Indolo[3,2,1‐jk]carbazole

AbstractThe multiple resonance thermally activated delayed fluorescence (MR‐TADF) materials can meet the requirement of a high color gamut of displays due to their narrowband emission. However, most reported organic light‐emitting diodes (OLEDs) based on MR‐TADF materials suffer from severe efficiency roll‐off. Herein, three green MR‐TADF emitters, p‐ICz‐BNCz, m‐ICz‐BNCz, and dm‐ICz‐BNCz, are obtained by introducing bulky indolo[3,2,1‐jk]carbazole (ICz) units into the classical DtBuCzB skeleton at the para or meta positions relative to the boron‐substituted phenyl ring. Compared with the para‐substitution of ICz, the meta‐substitution not only increases the reverse intersystem crossing rate constants of m‐ICz‐BNCz and dm‐ICz‐BNCz by nearly three times, but also makes their configurations more twisted. The two factors work together to improve the utilization of triplet excitons of the emitters, showing photoluminescence quantum yields exceeding 90%. As a result, the two corresponding OLEDs exhibit maximum external quantum efficiency (EQEmax) values of 28% and 32.9%, respectively, with low‐efficiency roll‐off. At the high brightness of 1000 cd m−2, the EQE values of the two devices still maintain at 19.3% and 25.0%, respectively. In addition, green emissions with Commission Internationale de l'Eclairage coordinates of (0.20, 0.70) and (0.30, 0.67) are also observed.

Uniformity improvement of a mini-LED backlight by a quantum-dot color conversion film with nonuniform thickness.

Mini-LED backlights energized by quantum-dot color conversion (QDCC) hold great potential for technological breakthroughs of liquid crystal displays. However, luminance uniformity issues should still be urgently solved owing to the large interval of direct-lit mini-LEDs, especially when covering with a QDCC film (QDCCF) with uniform thickness. Herein, we propose a uniformity improvement approach of mini-LED backlights by employing a QDCCF with nonuniform thickness based on the Lambertian distribution of mini-LEDs, which is demonstrated by screen-printing preparation and ray-tracing simulation. Experimental results show that the luminance uniformity of the nonuniform QDCCF can reach 89.91%, which is 24.92% higher than the uniform one. Ray-tracing simulation further elaborates the mechanism of this significant improvement. Finally, by employing this nonuniform QDCCF, a mini-LED backlight prototype is assembled and achieves high uniformity of 92.15%, good white balance with color coordinates of (0.3482, 0.3137), and high color gamut of 109% NTSC. This work should shed some new light on mini-LED-based display technology.

Low fluorescence crosstalk patterning of quantum dots based on laser drilling and micropore filling

In this study, a dual-color patterned perovskite quantum dot color conversion layer with a light-blocking matrix was created by combining laser drilling with micropore filling technology. When the blue micro-LED and the quantum dot color conversion layer make contact, the fluorescence crosstalk effect can be simulated to be near zero. The color conversion layers with high color gamut (111.2% of the National Television System Commission) were further confirmed to have outstanding optical isolation performance through experimental observations. This work may have significant advantages for its applications in photonic integration, micro-LED, and near-field displays due to simple operation process, maskless, harmlessness to quantum dots, short process period, and low crosstalk effect.

Synergistic Halide- and Ligand-Exchanges of All-Inorganic Perovskite Nanocrystals for Near-Unity and Spectrally Stable Red Emission.

All-inorganic perovskite nanocrystals (NCs) of CsPbX3 (X = Cl, Br, I) are promising for displays due to wide color gamut, narrow emission bandwidth, and high photoluminescence quantum yield (PLQY). However, pure red perovskite NCs prepared by mixing halide ions often result in defects and spectral instabilities. We demonstrate a method to prepare stable pure red emission and high-PLQY-mixed-halide perovskite NCs through simultaneous halide-exchange and ligand-exchange. CsPbBr3 NCs with surface organic ligands are first synthesized using the ligand-assisted reprecipitation (LARP) method, and then ZnI2 is introduced for anion exchange to transform CsPbBr3 to CsPbBrxI3-x NCs. ZnI2 not only provides iodine ions but also acts as an inorganic ligand to passivate surface defects and prevent ion migration, suppressing non-radiative losses and halide segregation. The luminescence properties of CsPbBrxI3-x NCs depend on the ZnI2 content. By regulating the ZnI2 exchange process, red CsPbBrxI3-x NCs with organic/inorganic hybrid ligands achieve near-unity PLQY with a stable emission peak at 640 nm. The CsPbBrxI3-x NCs can be combined with green CsPbBr3 NCs to construct white light-emitting diodes with high-color gamut. Our work presents a facile ion exchange strategy for preparing spectrally stable mixed-halide perovskite NCs with high PLQY, approaching the efficiency limit for display or lighting applications.

High‐Performance Narrowband OLED with Low Efficiency Roll‐Off Based on Sulfur‐Incorporated Organoboron Emitter

AbstractMulti‐resonance (MR) based organoboron emitters exhibiting high‐efficiency narrowband thermally activated delayed fluorescence (TADF) have become a critical material component for constructing high‐performance organic light‐emitting diodes (OLEDs) with high color purity and high color gamut. However, most of the MR‐TADF devices suffer from severe efficiency roll‐off at high current density due to the relatively large singlet–triplet splitting energy, long excited state lifetime, and slow reverse intersystem crossing rate (k RISC). Herein, by utilizing a sulfur atom‐fused donor unit, 7H‐benzo[4,5]thieno[2,3‐b]carbazole, an organic boron emitter (BTC‐BNCz) capable of high efficiency and low efficiency roll‐off narrowband TADF emission is developed. Benefitting from the heavy atom effect of the sulfur atom, kRISC up to 1.6 × 105 s−1 is achieved, which could greatly reduce the undesired quenching effect. Consequently, the OLED using BTC‐BNCz as dopant exhibits high external quantum efficiency (EQE) of 27.0% with full width at half maximum (FWHM) of 35 nm. Moreover, by utilizing a TADF material with a high horizontal dipole ratio as assistant host, outstanding device performance is achieved with a maximum EQE of 35.2% and FWHM of 37 nm, featuring slow efficiency roll‐off.

Brightened Bicomponent Perovskite Nano-Composite Based on Förster Resonance Energy Transfer for Micro-LED Displays.

The lead halide perovskite quantum dots (PQDs) is making its way towards next-generation display applications, such as serving as color conversion layers (CCL) in micro-LED array. Red PQDs containing iodine exhibit weaker brightness compared with its green counterpart when it is employed as CCL. Therefore, PQDs with enhanced brightness is highly favorable for micro/mini-LED displays. Wepropose a universal strategy of bicomponent perovskite nano-composite (BPNC) with significantly enhanced PL intensity through the built-in Förster resonance energy transfer (FRET) from the core CsPbBr3 to the shell γ-CsPbI3 , and confirm that it is through a pair of combined quasi-degenerate energy levels at blue spectra region that the FRET is conducted, resulting in a high excitation wavelength selectivity. Owing to the high-efficient energy transition route from blue excitation to red emission established by the FRET, the BPNC exhibits brightest single-peak red photoluminescence with near 100% quantum yield. The BPNC with FRET is further proven to be adaptable to a wide range of emission wavelength. Weemployed the BPNCs in a blue micro-LED array as color down-conversion layers and demonstrate excellent color conversion properties and high color gamut. This strategy of BPNC paves a road to the full-color micro-LEDdisplays. This article is protected by copyright. All rights reserved.

P‐112: Improvement of White OLED Performance by Optical Enhancement Structure

According to the demand of image quality improvement, the color gamut standard has been adjusted from DCI‐P3 to BT.2020. At present, the color gamut of some QD products can reach 80%~90%, while that of white OLED products is only about 75%. In this paper, the composite film with SiO2/SiNX distributed Bragg resonator (DBR) structure is designed and studied. The results show that the film can form a strong microcavity structure with simultaneous enhancement of RGB for white OLED devices, which overcomes the bottleneck that the strong microcavity structure can't be used in white OLED devices. It can effectively improve the performance of OLED devices, and at the same time, it has the water vapor barrier effect. It can realize the integration of multiple effects such as high color gamut, low power consumption and reliability improvement in product applications. Using the refractive index difference of SiO2/SiNx thin film, the DBR structure was fabricated by carefully designing the thickness. Based on this DBR structure, a white OLED device is fabricated. The external quantum efficiency of the device is improved, and the color gamut is up to 85% ( BT.2020), which is 11.2% higher than that of the device without DBR structure. Compared with the device without DBR structure, it has reached the QD display level, and the white light power consumption is reduced by 34.1%, HDR power consumption is reduced by 20.3%, and the overall performance is greatly improved. It provides technical support for products with high color gamut, low power consumption and long life.

Methylammonium Cation-Regulated Controllable Preparation of CsPbBr3 Perovskite Quantum Dots in Polystyrene Fiber with Enhanced Water and UV Light Stabilities

In situ fabrication of lead halide perovskite quantum dots (PQDs) is important for narrow-band emitters for LED displays due to the simple work procedure and convenient usability; however, the growth of PQDs is not readily controllable in the preparation, resulting in low quantum efficiency and environmental instability of PQDs. Here, we demonstrate an effective strategy to controllably prepare CsPbBr3 PQDs in polystyrene (PS) under the regulation of methylammonium bromide (MABr) via electrostatic spinning and thermal annealing techniques. MA+ slowed down the growth of CsPbBr3 PQDs and acted as a surface defect passivation reagent, which was proved by Gibbs free energy simulation, static fluorescence spectra, transmission electron microscopy, and time-resolved photoluminescence (PL) decay spectra. Among a series of prepared Cs1-xMAxPbBr3@PS (0 ≤ x ≤ 0.2) nanofibers, Cs0.88MA0.12PbBr3@PS shows the regular particle morphology of CsPbBr3 PQDs and the highest photoluminescence quantum yield of up to 39.54%. The PL intensity of Cs0.88MA0.12PbBr3@PS is 90% of the initial intensity after immersing in water for 45 days and 49% of the initial value after persistent ultraviolet (UV) irradiation for 27 days. A high color gamut containing 127% of the National Television Systems Committee standard with long-time working stability was also obtained on light-emitting diode package measurements. These results demonstrate that MA+ can effectively control the morphology, humidity, and optical stability of CsPbBr3 PQDs in the PS matrix.

Constructing physical space design for high color gamut in mixed reality environment

This paper presents a physical space design method for mixed reality-based immersive environments by improving the color rendering of optically visible head-mounted displays. In OST-HMD, the phenomenon that the light of the external environment is combined with the enhanced image occurs, which reduces the visibility of the content. Moreover, previous studies to solve this problem required additional optical components or performed only simple verification. Proposed physical space was designed using black curtains, blinds, low-reflection structures, and adjustable lighting. The physical space can be adapted to the intended use of the physical space through physical transitions for multiple users without additional optics. To verify the usefulness of this environment, we measured the color gamut and intensity spectrum in three experimental environments. Also, we analyzed the factors that change the color gamut according to the components and the surrounding environment. As a result, the color gamut improved by up to 4.7 times from 19.92% to 93.53% based on the environment and improved by up to 4.1 times from 21% to 86.29% depending on the location. The experimental results revealed that the presented method could reduce the factors that degrade the color gamut within all measurement locations and significantly improve the color gamut.

P‐17.1: Research on Halo Effect in Mini LED Backlight

In recent years, with the improvement of consumers' pursuit of display quality, in the field of LCD display, the direct‐light backlight technology is increasingly used in TV, MNT, NB, VR, Pad and even automotive display fields. Using this technology to zone the backlight can achieve local dimming technology, that is, adjust the brightness of the single backlight zone according to the image. Thus, high contrast ratio and high color gamut can be achieved while reducing power consumption. However, compared with the traditional edge‐light display, the halo effect of the direct‐light backlight display greatly affects the visual effect. At present, backlight design tends to be highly zoned, which will affect the halo effect and contrast ratio. And as customers pursue further improvement in optical property, the 3D reflector design to enhance the luminance of the single zone will also affect contrast ratio and halo effect. In this paper, we explored the influence of zone size and 3D reflector design on halo effect and contrast ratio, so as to guide the subsequent products to carry out appropriate zone size design.

Luminous Properties of Red, Green, and Blue Micro-LEDs and the Impacts on Color Gamut

Electrical-chromatic characteristics of red, green, and blue micro-LEDs (10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m) are investigated at temperatures ranging from 300 to 340 K. The external quantum efficiency (EQE) of red micro-LEDs decreases significantly with the increasement in temperature, suggesting that heat dissipation is crucial for red micro-LEDs. The impacts of temperature and driving current on the chromaticity coordinates of the light emission from micro-LEDs are determined. When the trichromatic micro-LEDs are driven by the currents corresponding to the maximum EQE, the influence of temperature on the color gamut is limited, facilitating the achievement of high color gamut and high efficiency.

Quantum dots printing paste for display backlights: Preparation, characterization, and applications

AbstractQuantum dots (QDs) are one kind of photoluminescent materials with excellent properties, such as adjustable spectrum, narrow full width at half maximum (FWHM), and high color gamut. In this paper, a photoluminescent QDs printing paste suitable for light guide dots array applied in the backlight for liquid crystal display (LCD) was presented. The QDs printing paste was first prepared and characterized with different kinds of solvents. Then, triphenyl phosphite (TPP), a kind of antioxygen, was added into the QDs printing paste to improve the stability of the QDs printing paste. Finally, a QDs light guide plate (LGP) was fabricated by screen printing with QDs printing paste added with silicon dioxide (SiO2) light scattering particles. The color gamut of QDs LGP arrived 131.6%NTSC due to light scattering interaction between blue LED, red QDs, green QDs, and SiO2 particles. The results showed that the QDs‐chloroform printing paste had uniform light output and the highest photoluminescent peak intensity. Therefore, the composite screen printing paste has wide application prospects in the backlight of LCD, with the advantages of simple process, high production efficiency, and low cost.

Mediation of exciton concentration on magnetic field effects in NPB : Alq3-based heterojunction OLEDs.

Organic light-emitting diodes (OLEDs) are considered one of the most promising new display technologies owing to their advantages, such as all-solid-state, high color gamut, and wide viewing angle. However, in terms of special fields, the brightness, lifetime, and stability of the devices need further improvement. Therefore, heterojunction devices with different concentrations were prepared to regulate device brightness. The brightness of the bulk heterojunction device is enhanced by 9740 cd m-2, with a growth rate of about 26.8%. The impact of various temperatures and various exciton concentrations on the device magneto-conductance (MC) and magneto-electroluminescence (MEL) was investigated. Experimental results demonstrate that the exciton concentration inside the device can be tuned to improve optoelectronic properties and organic magnetic effects. The complex spin mixing process inside the bulk heterojunction device is deeply investigated, which provides a reliable basis for the design of bulk heterojunction devices.

Comparison of different RGB InP-quantum-dot-on-chip LED configurations.

InP/ZnSe/ZnS quantum dots (QDs) offer a cadmium-free solution to make white LEDs with a narrow blue, green and red emission peak. Such LEDs are required for display and lighting applications with high color gamut. An important phenomenon that hampers the efficiency of such quantum-dot-on-chip LEDs is re-absorption of already converted light by the QDs. Proposed solutions to remedy this effect often rely on complex or cost-ineffective manufacturing methods. In this work, four different RGB QD-on-chip LED package configurations are investigated that can be fabricated with a simple cavity encapsulation method. Using accurate optical simulations, the impact of QD re-absorption on the overall luminous efficacy of the light source is analyzed for these four configurations as a function of the photo-luminescent quantum yield (PLQY) of the QDs. The simulation results are validated by implementing these configurations in QD-on-chip LEDs using a single set of red and green emitting InP/ZnSe/ZnS QDs. In this way, the benefits are demonstrated of adding volume scattering particles or a hemispherical extraction dome to the LED package. The best configuration in terms of luminous efficacy, however, is one where the red QDs are deposited in the recycling cavity, while the green QDs are incorporated in the extraction dome. Using this configuration with green and red InP/ZnSe/ZnS QDs with a PLQY of 75% and 65% respectively, luminous efficacy of 102 lm/W was realized for white light with a CCT of 3000 K.

34.2: Invited Paper: High Image Quality ADS PRO TV Comparable to OLED

ADS display mode has many advantages, especially wide viewing angle, and has been widely used in various LCD products. In this paper, based on the upgraded ADS PRO technology, we adopt high CR negative liquid crystal, low reflection surface materials and process, oblique angle light leakage compensation film, spectrum matching optimize of BLU and RGB resin, and combined with mini LED backlight. Based on these methods, we achieve the native CR &gt;3000:1, extreme black state with reflectivity &lt; 1.5%, high ambient color contrast, no color shift angle of &gt; ±60 °, and DCI P3 99% high color gamut. Its ultimate picture quality can be equivalent to OLED.

P‐3.14: Development of Thin Film Design based on IGZO‐TFT Displays for Transmittance and Picture Quality Improvement

P‐3.14: Development of Thin Film Design based on IGZO‐TFT Displays for Transmittance and Picture Quality Improvement