Figure - available via license: Creative Commons Attribution 4.0 International
Content may be subject to copyright.
Source publication
Color-converted micro-light-emitting diode (micro-LED) displays with wide color gamut, high ambient contrast ratio, and fast response time are emerging as a potentially disruptive technology. However, due to limited optical density and thickness of the color-conversion film, the blue light leakage and low color-conversion efficiency still hinder th...
Context in source publication
Context 1
... Inc., Santa Clara, CA, USA) to simulate the performance of our proposed display system. The size of the LED chip used in our simulation model is 100 µm × 100 µm, and Table 1 lists the material properties of the flip-chip blue LED at three specified wavelengths. The radiation pattern of blue micro-LED emitted from the molding layer is plotted in Figure 4a. ...Citations
... This is due to the different refractive indices of the two different material systems and the sidewall emission of the devices. The angular shift problems have been discussed in some micro-LED articles [21,22], but were seldom mentioned in QD on micro-LED structure. Hence, in this study, we will first place the QD composite on top of the device, which could have a stronger thermal influence on these nanocrystals. ...
Colloidal CdSe/ZnS quantum dots (QD) enhanced micro-LEDs with sizes varying from 10 to 100 μm were fabricated and measured. The direct photolithography of quantum-dot-contained photoresists can place this color conversion layer on the top of an InGaN-based micro-LED and have a high throughput and semiconductor-grade precision. Both the uncoated and coated devices were characterized, and we determined that much higher brightness of a QD-enhanced micro-LED under the same current level was observed when compared to its AlGaInP counterpart. The color stability across the device sizes and injection currents were also examined. QD LEDs show low redshift of emission wavelength, which was recorded within 1 nm in some devices, with increasing current density from 1 to 300 A/cm2. On the other hand, the light conversion efficiency (LCE) of QD-enhanced micro-LEDs was detected to decrease under the high current density or when the device is small. The angular intensities of QD-enhanced micro-LEDs were measured and compared with blue devices. With the help of the black matrix and omnidirectional light emission of colloidal QD, we observed that the angular intensities of the red and blue colors are close to Lambertian distribution, which can lead to a low color shift in all angles. From our study, the QD-enhanced micro-LEDs can effectively increase the brightness, the color stability, and the angular color match, and thus play a promising role in future micro-display technology.
... Micro-LEDs (LEDs with sizes <100 µm [1]) are used in self-emitting displays, especially micro-projection displays. The contrast, efficiency, resolution, and response time of a micro-LED are typically high, and micro-LED displays outperform LCD and OLED displays in terms of brightness, resolution, contrast, energy consumption, service life, response speed, and thermal stability [2]. ...
... Micro-LED chips produce a more even distribution; developing highly homogeneous micro-LED optical-design technology is therefore an urgent scientific and technological challenge. Direct measurements have shown that the secondary light distribution curve of micro-LEDs is non-Lambertian [1,2,5]. Bayneva [21] simulated the light distribution using Tracepro. ...
... Bayneva [21] simulated the light distribution using Tracepro. They applied the ray-tracing method in the early stages and found that as the size of the micro-LED decreased, the micro-LED far-field light distribution stopped following a Lambertian distribution [1,22]. ...
To clarify how micro-LED far-field light distributions differ from Lambertian distributions owing to small-sized-structure effects, the light distribution of a micro-LED was simulated via the ray-tracing method in this study. Specifically, considering material absorption, far-field light distribution, and light-output efficiency, we studied micro-LEDs as a function of size. We found that the light distribution is the most uniform and the efficiency is the highest when the size is the smallest under certain conditions. Under other conditions, with increasing sapphire size, the luminous efficiency first increases and then decreases. The luminous efficiency is the highest when the thickness is 30 µm. Under certain other conditions, as the diameter of the micro-sphere structure on the sapphire increases, the luminous efficiency first increases and then decreases.
... When compared, as in the insets of Figure 4b,c, 8 mg/mL-based AuAg NP polymeric film was found to be superior in the suppression of blue light leakage to LCD color filters for both green and red color-by-blue tests. In the color-by-blue mode-based display device where QD emitters are placed in the front panel, QDs can be undesirably excited upon exposure to ambient lights [31,32]. This inevitably deteriorates the color purity and contrast ratio of the display device. ...
... Furthermore, the same measurement as in Figure 5c was carried out for red QD film/AuAg NP film stacks, showing an identical trend in AuAg NP concentration-dependent spectral evolutions of reflected blue excitation and QD emissions (Figure 5d). In the color-by-blue mode-based display device where QD emitters are placed in the front panel, QDs can be undesirably excited upon exposure to ambient lights [31,32]. This inevitably deteriorates the color purity and contrast ratio of the display device. ...
In typical color-by-blue mode-based quantum dot (QD) display devices, only part of the blue excitation light is absorbed by QD emitters, thus it is accompanied by the leakage of blue light through the devices. To address this issue, we offer, for the first time, the applicability of AuAg alloy nanoparticles (NPs) as effective blue light absorbers in InP QD-based color-by-blue platforms. For this, high-quality fluorescent green and red InP QDs with a double shell scheme of ZnSe/ZnS were synthesized and embedded in a transparent polymer film. Separately, a series of Au/Ag ratio-varied AuAg NPs with tunable plasmonic absorption peaks were synthesized. Among them, AuAg NPs possessing the most appropriate absorption peak with respect to spectral overlap with blue emission are chosen for the subsequent preparation of AuAg NP polymeric films with varied NP concentrations. A stack of AuAg NP polymeric film on top of InP QD film is then placed remotely on a blue light-emitting diode, successfully resulting in systematically progressive suppression of blue light leakage with increasing AuAg NP concentration. Furthermore, the beneficial function of the AuAg NP polymeric overlayer in mitigating undesirable QD excitation upon exposure to ambient lights was further examined.
... In order to meet the current criterion, micro-LED is required to reduce the single-pixel size down to less than 100 µm [1]. Hence, how to achieve full-color display down to microscale has become a significant issue for micro-LED [2][3][4]. Mass transfer and epitaxial growth for fabricating full-color (RGB) micro-LED are difficult. Fortunately, quantum dots (QDs) can absorb blue light to generate color-converted red and green light, making them ideal for full-color micro-LED display [5,6]. ...
This work demonstrated color-conversion layers of red and green quantum dots color filter for full-color display arrays. Ligands exchange using (3-glycidyloxypropyl) trimethoxysilane with epoxy functional groups to treat QDs in the liquid phase was performed for photolithography use. The combination of ligands of QDs with photo-initiator played a protective role on QDs. Moreover, the pixel size of green QDCF can be reduced to 50 μm, and a high optical density (OD) of 1.2 is realized.
... At the mass-production stage, the QDs would be integrated on a planarized surface of GaN LEDs coated with peripheral layers (e.g., distributed Bragg reflector (DBR) layer or a black matrix layer in between mesas) to reduce optical crosstalk and improve the color purity. While the main focus of this work is the experimental demonstration of color conversion and highresolution patterning of QDs, the effect of a DBR layer on color purity is quite important 80,81 . Hence the effect of using a DBR on the QDs and LEDs was studied and shown in Supplementary Fig. S8 and S9. ...
Near-eye display technology is a rapidly growing field owing to the recent emergence of augmented and mixed reality. Ultrafast response time, high resolution, high luminance, and a dynamic range for outdoor use are all important for non-pixelated, pupil-forming optics. The current mainstream technologies using liquid crystals and organic materials cannot satisfy all these conditions. Thus, finely patterned light-emissive solid-state devices with integrated circuits are often proposed to meet these requirements. In this study, we integrated several advanced technologies to design a prototype microscale light-emitting diode (LED) arrays using quantum dot (QD)-based color conversion. Wafer-scale epilayer transfer and the bond-before-pattern technique were used to directly integrate 5-µm-scale GaN LED arrays on a foreign silicon substrate. Notably, the lithography-level alignment with the bottom wafer opens up the possibility for ultrafast operation with circuit integration. Spectrally pure color conversion and solvent-free QD patterning were also achieved using an elastomeric topographical mask. Self-assembled monolayers were applied to selectively alter the surface wettability for a completely dry process. The final emissive-type LED array integrating QD, GaN, and silicon technology resulted in a 1270 PPI resolution that is far beyond the retinal limit.
... As shown in Figure 2a, to improve the excitation light absorption, a high-pass filter recycles the blue light leaked from the QDCC back to the film to excite the QD material, and the absorption filters on top of the QDCC prevents blue light leakage and eliminates ambient light excitation. 57,58 The band-pass filter can be a distributed Bragg reflector (DBR) or a stacked cholesteric liquid crystal (CLC) film with opposite chirality. ...
Luminescent quantum dots (QDs) and perovskite nanocrystals (PNCs) are promising, efficient energy converters for advanced displays and light sources. Their widespread applications in the photoluminescence (PL)-based displays have been achieved through color enhancement films and patterned color-converters. Meanwhile, electroluminescence (EL) devices based on QDs and PNCs are still under active development, but emerging applications in the healthcare domains could accelerate their adoption. Herein, we first analyze the QD color-conversion displays guided by state-of-the-art research and then summarize the evolution of in situ strategies to fabricate efficient and stable PNC–polymer composites. Subsequently, we introduce the application of flexible QD light-emitting devices for healthcare as a potential early target market. Remaining challenges and future perspectives of QDs and PNCs as light-converters for PL displays, and of QDs for EL applications in healthcare, are analyzed.
... Polarizer, an indispensable element in modern displays, has been widely applied in various different kinds of displays to obtain different functions, and its performance is a key parameter that impacts the display quality [1][2][3][4]. In liquid crystal displays (LCD), two polarizers, crossed polarizer and analyzer, are the basis of the optical switching function. ...
The polarizer is an indispensable element in modern displays, but the azimuthal transmittance variation of the polarizer also affects the display quality, and it is hard to eliminate the azimuthal transmittance variation because of the polarizer’s structure. In this paper, we propose a multi-layer composite polarizer with polarizing layer – twisted nematic liquid crystal polymer layer – polarizing layer structure. An iodide molecule distribution model is introduced to explain the azimuthal transmittance variation of the normal polarizer and guide the design of the multi-layer composite polarizer. The azimuthal transmittance variation of the multi-layer composite polarizer and normal polarizer is measured and calculated, and the results show that the azimuthal transmittance variation of the multi-layer composite polarizer is only about one-fifth of that of the normal polarizer. Except for the most uniform transmittance distribution, the transmittance distribution of the multi-layer composite polarizer can be adjusted to meet different requirements. The potential concerns about low transmittance and color shift are also discussed, and they can be solved by reducing the polarization degree of the polarizing layers and increasing the thickness of the liquid crystal polymer layer. The results show that the multi-layer composite polarizer can replace the normal polarizer to reduce the viewing angle defects of the emissive displays.
... Polarizer, an indispensable element in modern displays, has been widely applied in various different kinds of displays to obtain different functions, and its performance is a key parameter that impacts the display quality [1][2][3][4]. In liquid crystal displays (LCD), two polarizers, crossed polarizer and analyzer, are the basis of the optical switching function. ...
We demonstrate a wide viewing angle polarization interference filter (PIF), which consists of two crossed polarizers and double liquid crystal layers with opposite twisted direction. The polarization interference effect of the PIF is achieved by the double liquid crystal layers, and an additional compensation layer between the double liquid crystal layers can further improve the optical performance of the PIF. By using the Jones matrix method, we derive the transmittance formula of the PIF with/without compensation layer, which can be used to design any required color filter by selecting the appropriate twist angle and thickness of the liquid crystal layer. We design blue, green and red PIFs and analyze their optical performance. The proposed PIF has a wider viewing angle (±30°), and the color saturation of the PIF is also considerably high.
... Multi-domain periodical LC structure can be applied in many display fields including holographic polarizers [75], CMOS polarization image sensor [76], and LC displays [77,78]. To photo-align the pixelated PG structure where each pixel governs a PG domain with independent grating vector, many methods were proposed such as multi-time rubbing, multi-step interference, building the nanostructure on the surface using the imprint method, or digital method as presented in Section 3.2.3. ...
Liquid crystal (LC) circular polarization gratings (PGs), also known as Pancharatnam–Berry (PB) phase deflectors, are diffractive waveplates with linearly changed optical anisotropy axes. Due to the high diffraction efficiency, polarization selectivity character, and simple fabrication process, photoalignment LC PGs have been widely studied and developed especially in polarization management and beam split. In this review paper, we analyze the physical principles, show the exposure methods and fabrication process, and present relevant promising applications in photonics and imaging optics.
... The pitch of the helix structure is sensitive to various external fields (light [6], electrical [7,8], thermal [9] and so on [10,11]) allowing flexible tuning of the cholesteric stop band. These features of CLC have allowed various photonic devices such as tunable color filters [12] and LED displays with wide color gamut [13] to be designed. ...
Hybrid fluorescent cholesteric liquid crystalline (CLC) materials are representatives of “smart” soft matter, and are characterized by light emission that can be flexibly controlled by various external stimuli. This fact is due to the many possibilities for potential applications in the fields of photonics and optics stimulating design, and study of this type of hybrid materials. Here, we report on the optical and fluorescence properties of the hybrid CLC material based on a low-molecular-weight CLC matrix and CdSe/ZnS quantum dots (QDs) stabilized by LC diblock copolymers. The hybrid CLC material is characterized by the cholesteric phase in a wide temperature range, the high loading of QDs, and no QD aggregation. We demonstrate that the cholesteric stop band alters characteristics of the QD emission due to the resonance effect. This makes the polarization state and wavelength of the QD emission thermo- and angle-dependent. This work provides a way for the design of a wide range of field-controllable photonic devices for various applications.
