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Quantum Dots and Micro-LED Display

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A special issue of Nanomaterials (ISSN 2079-4991).

Deadline for manuscript submissions: closed (31 October 2020) | Viewed by 77028

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Prof. Dr. Hao-Chung Kuo

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Guest Editor

Department of Photonics, College of Electrical and Computer Engineering, National Chiao Tung University, 1001 Ta Hsueh Rd., Hsinchu 300, Taiwan
Interests: nanostructured optoelectronic materials and devices; III-V (nitride) high speed semiconductor laser technology and related research
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Prof. Dr. Lung-Chien Chen

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Co-Guest Editor

Department of Electro-Optical Engineering, National Taipei University of Technology, Taipei, Taiwan
Interests: epitaxial technology (MOCVD, LPE, and spray methods); compound semiconductors/fabrication and analysis of transparent conducting oxide semiconductors; fabrication of light-emitting diodes; fabrication of solar cells; nanomaterial processes; fabrication of sensor devices; fabrication of perovskite quantum dots; fabrication of perovskite optoelectronic devices (QLEDs, solar cells, and sensors)
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Prof. Dr. Zhaojun Liu

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Co-Guest Editor

Department of Electrical and Electronic Engineering, Southern University of Science and Technology, Qingshuihe, Shenzhen, China
Interests: micro-LEDs; advanced displays and AR/VR; mass transferring and advanced packaging; GaN transistors and LEDs; wearable devices
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Quantum dots (QDs) have many unique physical and optical properties, such as high photoluminescence quantum yield, tunable emission over the entire visible spectral region, narrow emission spectrum, and high color purity. QDs have become a suitable candidate material in the display field, which has great potential to replace the traditional phosphor powder and increase the LCD color gamut range.

Micro-LED is an emerging flat panel display technology. As the name implies, micro LED displays consist of arrays of microscopic LEDs forming the individual pixel elements. The applications include near-eye display, wearable devices, head mount devices, visible light communications, computer monitors, biomedical devices and projectors, which are benefit from the obvious advantages of Micro-LED display in brightness and saturation, high display quality even in high-intensity ambient light.

In this Special Issue, we would like to invite all papers related science and technologies of Quantum Dot (QD) ranging from materials research, device structure and properties, device applications for micro-LED display, manufacturing and high color gamut of display using QD. Especially, in the following fields:

QD or Micro-LED display
Energy applications
Bio-applications
Mechanical resonators
Optoelectronics like lasing, lighting, micro-display, AR/VR etc.

Prof. Dr. Hao-chung Kuo
Prof. Dr. Lung-Chien Chen
Prof. Dr. Zhaojun Liu
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Nanomaterials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2900 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Nanomateria
Perovskite quantum dots
IR quantum dots
microled display

Published Papers (12 papers)

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Research

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14 pages, 7831 KiB

Open AccessArticle

Enhancing the Efficiency of Color Conversion Micro-LED Display with a Patterned Cholesteric Liquid Crystal Polymer Film

by En-Lin Hsiang, Yannanqi Li, Ziqian He, Tao Zhan, Caicai Zhang, Yi-Fen Lan, Yajie Dong and Shin-Tson Wu

Nanomaterials 2020, 10(12), 2430; https://doi.org/10.3390/nano10122430 - 05 Dec 2020

Cited by 28 | Viewed by 5027

Abstract

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 their widespread applications. In this paper, we demonstrate a patterned cholesteric liquid crystal (CLC) polymer film with two special optical functionalities. On the green and red sub-pixels, the corresponding planar CLC texture acts as a distributed Bragg reflector for the blue light, which in turn improves the color conversion efficiency and expands the color gamut. On the blue sub-pixels, the corresponding focal-conic CLC texture acts as light scattering medium, which helps to reduce the angular color shift. Further analysis reveals that the patterned CLC film can alleviate the crosstalk between green and blue color filters. Therefore, compared to the display system without such a CLC film, our proposed device structure increases the color conversion efficiency by 143% (at ~90% Rec. 2020) and reduces average angular color shift Δu’v’ from 0.03 to 0.018 at the viewing angle with the most severe color shift. Such a patterned CLC film is applicable to all kinds of color-conversion display systems, including organic and inorganic phosphors. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display)

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10 pages, 2646 KiB

Open AccessArticle

Dependence of Photoresponsivity and On/Off Ratio on Quantum Dot Density in Quantum Dot Sensitized MoS₂ Photodetector

by Yung-Yu Lai, Yen-Wei Yeh, An-Jye Tzou, Yi-Yuan Chen, YewChung Sermon Wu, Yuh-Jen Cheng and Hao-Chung Kuo

Nanomaterials 2020, 10(9), 1828; https://doi.org/10.3390/nano10091828 - 14 Sep 2020

Cited by 13 | Viewed by 3104

Abstract

Non-radiative energy transfer (NRET) from quantum dots (QDs) to monolayer MoS₂ has been shown to greatly enhance the photoresponsivity of the MoS₂ photodetector, lifting the limitations imposed by monolayer absorption thickness. Studies were often performed on a photodetector with a channel length of only a few μm and an active area of a few μm². Here, we demonstrate a QD sensitized monolayer MoS₂ photodetector with a large channel length of 40 μm and an active area of 0.13 mm². The QD sensitizing coating greatly enhances photoresponsivity by 14-fold at 1.3 μW illumination power, as compared with a plain monolayer MoS₂ photodetector without QD coating. The photoresponsivity enhancement increases as QD coating density increases. However, QD coating also causes dark current to increase due to charge doping from QD on MoS₂. At low QD density, the increase of photocurrent is much larger than the increase of dark current, resulting in a significant enhancement of the signal on/off ratio. As QD density increases, the increase of photocurrent becomes slower than the increase of dark current. As a result, photoresponsivity increases, but the on/off ratio decreases. This inverse dependence on QD density is an important factor to consider in the QD sensitized photodetector design. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display)

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8 pages, 1859 KiB

Open AccessArticle

Comparative Chemico-Physical Analyses of Strain-Free GaAs/Al_0.3Ga_0.7As Quantum Dots Grown by Droplet Epitaxy

by Inah Yeo, Doukyun Kim, Kyu-Tae Lee, Jong Su Kim, Jin Dong Song, Chul-Hong Park and Il Ki Han

Nanomaterials 2020, 10(7), 1301; https://doi.org/10.3390/nano10071301 - 02 Jul 2020

Cited by 6 | Viewed by 2550

Abstract

We investigate the quantum confinement effects on excitons in several types of strain-free GaAs/Al

_{0.3}

_{0.7}

We investigate the quantum confinement effects on excitons in several types of strain-free GaAs/Al

_{0.3}

_{0.7}

As droplet epitaxy (DE) quantum dots (QDs). By performing comparative analyses of energy-dispersive X-ray spectroscopy with the aid of a three-dimensional (3D) envelope-function model, we elucidate the individual quantum confinement characteristics of the QD band structures with respect to their composition profiles and the asymmetries of their geometrical shapes. By precisely controlling the exciton oscillator strength in strain-free QDs, we envisage the possibility of tailoring light-matter interactions to implement fully integrated quantum photonics based on QD single-photon sources (SPSs). Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display)

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9 pages, 2097 KiB

Open AccessArticle

Investigation of Electrical Properties and Reliability of GaN-Based Micro-LEDs

by Ke Zhang, Yibo Liu, Hoi-sing Kwok and Zhaojun Liu

Nanomaterials 2020, 10(4), 689; https://doi.org/10.3390/nano10040689 - 06 Apr 2020

Cited by 41 | Viewed by 4671

Abstract

In this paper, we report high-performance Micro-LEDs on sapphire substrates, with pixel size scaling to 20 µm and an ultra-high current density of 9902 A/cm². The forward voltages (V_F) of the devices ranged from 2.32 V to 2.39 V under an injection current density of 10 A/cm². The size and structure-dependent effects were subsequently investigated to optimize the device design. The reliability of Micro-LED devices was evaluated under long-aging, high-temperature, and high-humidity conditions. It was found that Micro-LED devices can maintain comparable performance with an emission wavelength of about 445 nm and a full width at half maximum (FWHM) of 22 nm under extreme environments. Following this, specific analysis with four detailed factors of forward voltage, forward current, slope, and leakage current was carried out in order to show the influence of the different environments on different aspects of the devices. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display)

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11 pages, 3640 KiB

Open AccessArticle

Yb:MoO₃/Ag/MoO₃ Multilayer Transparent Top Cathode for Top-Emitting Green Quantum Dot Light-Emitting Diodes

by Chun-Yu Lee, Yi-Min Chen, Yao-Zong Deng, Ya-Pei Kuo, Peng-Yu Chen, Leo Tsai and Ming-Yi Lin

Nanomaterials 2020, 10(4), 663; https://doi.org/10.3390/nano10040663 - 02 Apr 2020

Cited by 9 | Viewed by 3691

Abstract

In this study, we report on the application of a dielectric/ultra-thin metal/dielectric (DMD) multilayer consisting of ytterbium (Yb)-doped molybdenum oxide (MoO₃)/silver (Ag)/MoO₃ stacked as the transparent cathode in top-emitting green quantum dot light-emitting diodes (QLED). By optimizing the Yb doping ratio, we have highly improved the electron injection ability from 0.01 to 0.35. In addition, the dielectric/ultra-thin metal/dielectric (DMD) cathode also shows a low sheet resistance of only 12.2 Ω/sq, which is superior to the resistance of the commercially-available indium tin oxide (ITO) electrode (~15 Ω/sq). The DMD multilayer exhibits a maximum transmittance of 75% and an average transmittance of 70% over the visible range of 400–700 nm. The optimized DMD-based G-QLED has a smaller current leakage at low driving voltage. The optimized DMD-based G-QLED enhances the current density than that of G-QLED with indium zinc oxide (IZO) as a cathode. The fabricated DMD-based G-QLED shows a low turn-on voltage of 2.2 V, a high current efficiency of 38 cd/A, and external quantum efficiency of 9.8. These findings support the fabricated DMD multilayer as a promising cathode for transparent top-emitting diodes. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display)

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11 pages, 2106 KiB

Open AccessArticle

Spray Coated Colloidal Quantum Dot Films for Broadband Photodetectors

by Kaixuan Song, Jifeng Yuan, Ting Shen, Jiuyao Du, Ruiqi Guo, Tönu Pullerits and Jianjun Tian

Nanomaterials 2019, 9(12), 1738; https://doi.org/10.3390/nano9121738 - 06 Dec 2019

Cited by 10 | Viewed by 3314

Abstract

A technique for scalable spray coating of colloidal CdSeTe quantum dots (QDs) for photovoltaics and photodetector applications is presented. A mixture solvent with water and ethanol was introduced to enhance the adhesive force between QDs and the substrate interface. The performance of the detector reached the highest values with 40 spray coating cycles of QD deposition. The photodetectors without bias voltage showed broadband response in the wavelength range of 300–800 nm, and high responsivity of 15 mA/W, detectivity of more than 10¹¹ Jones and rise time of 0.04 s. A large size QD-logo pattern film (10 × 10 cm²) prepared by the spray coating process displayed excellent uniformity of thickness and absorbance. The large area detectors (the active area 1 cm²) showed almost the same performance as the typical laboratory-size ones (the active area 0.1 cm²). Our study demonstrates that the spray coating is a very promising film fabrication technology for the industrial-scale production of optoelectronic devices. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display)

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8 pages, 3032 KiB

Open AccessArticle

Influence of Annealing Temperature on Weak-Cavity Top-Emission Red Quantum Dot Light Emitting Diode

by Chun-Yu Lee, Ya-Pei Kuo, Peng-Yu Chen, Hsieh-Hsing Lu and Ming Yi Lin

Nanomaterials 2019, 9(11), 1639; https://doi.org/10.3390/nano9111639 - 19 Nov 2019

Cited by 10 | Viewed by 3791

Abstract

In this report, we show that the annealing temperature in QDs/Mg-doped ZnO film plays a very important role in determining QLEDs performance. Measurements of capacitance and single carrier device reveal that the change of the device efficiency with different annealing temperatures is related to the balance of both electron and hole injection. A comparison of annealing temperatures shows that the best performance is demonstrated with 150 °C-annealing temperature. With the improved charge injection and charge balance, a maximum current efficiency of 24.81 cd/A and external quantum efficiency (EQE) of 20.09% are achievable in our red top-emission QLEDs with weak microcavity structure. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display)

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11 pages, 3337 KiB

Open AccessArticle

Ultrawide Color Gamut Perovskite and CdSe/ZnS Quantum-Dots-Based White Light-Emitting Diode with High Luminous Efficiency

by Chih-Hao Lin, Chieh-Yu Kang, Akta Verma, Tingzhu Wu, Yung-Min Pai, Tzu-Yu Chen, Chun-Lin Tsai, Ya-Zhu Yang, S.K. Sharma, Chin-Wei Sher, Zhong Chen, Po-Tseng Lee, Shu-Ru Chung and Hao-Chung Kuo

Nanomaterials 2019, 9(9), 1314; https://doi.org/10.3390/nano9091314 - 14 Sep 2019

Cited by 21 | Viewed by 5026

Abstract

We demonstrate excellent color quality of liquid-type white light-emitting diodes (WLEDs) using a combination of green light-emitting CsPbBr₃ and red light-emitting CdSe/ZnS quantum dots (QDs). Previously, we reported red (CsPbBr_1.2I_1.8) and green (CsPbBr₃) perovskite QDs (PQDs)-based WLEDs with high color gamut, which manifested fast anion exchange and stability issues. Herein, the replacement of red PQDs with CdSe/ZnS QDs has resolved the aforementioned problems effectively and improved both stability and efficiency. Further, the proposed liquid-type device possesses outstanding color gamut performance (132% of National Television System Committee and 99% of Rec. 2020). It also shows a high efficiency of 66 lm/W and an excellent long-term operation stability for over 1000 h. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display)

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14 pages, 4040 KiB

Open AccessArticle

A Bilayer 2D-WS₂/Organic-Based Heterojunction for High-Performance Photodetectors

by Feng Huang, Jing Zhou Li, Zhu Hua Xu, Yuan Liu, Ri Peng Luo, Si Wei Zhang, Peng Bo Nie, Yan Fei Lv, Shi Xi Zhao, Wei Tao Su, Wen Di Li, Shi Chao Zhao, Guo Dan Wei, Hao Chung Kuo and Fei Yu Kang

Nanomaterials 2019, 9(9), 1312; https://doi.org/10.3390/nano9091312 - 13 Sep 2019

Cited by 21 | Viewed by 3965

Abstract

Two-dimensional (2D) tungsten disulfide (WS₂) has inspired great efforts in optoelectronics, such as in solar cells, light-emitting diodes, and photodetectors. However, chemical vapor deposition (CVD) grown 2D WS₂ domains with the coexistence of a discontinuous single layer and multilayers are still not suitable for the fabrication of photodetectors on a large scale. An emerging field in the integration of organic materials with 2D materials offers the advantages of molecular diversity and flexibility to provide an exciting aspect on high-performance device applications. Herein, we fabricated a photodetector based on a 2D-WS₂/organic semiconductor materials (mixture of the (Poly-(N,N′-bis-4-butylphenyl-N,N′-bisphenyl) benzidine and Phenyl-C61-butyric acid methyl ester (Poly-TPD/PCBM)) heterojunction. The application of Poly-TPD/PCBM organic blend film enhanced light absorption, electrically connected the isolated WS₂ domains, and promoted the separation of electron-hole pairs. The generated exciton could sufficiently diffuse to the interface of the WS₂ and the organic blend layers for efficient charge separation, where Poly-TPD was favorable for hole carrier transport and PCBM for electron transport to their respective electrodes. We show that the photodetector exhibited high responsivity, detectivity, and an on/off ratio of 0.1 A/W, 1.1 × 10¹¹ Jones, and 100, respectively. In addition, the photodetector showed a broad spectral response from 500 nm to 750 nm, with a peak external quantum efficiency (EQE) of 8%. Our work offers a facile solution-coating process combined with a CVD technique to prepare an inorganic/organic heterojunction photodetector with high performance on silicon substrate. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display)

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Review

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33 pages, 7517 KiB

Open AccessReview

Full-Color Realization of Micro-LED Displays

by Yifan Wu, Jianshe Ma, Ping Su, Lijun Zhang and Bizhong Xia

Nanomaterials 2020, 10(12), 2482; https://doi.org/10.3390/nano10122482 - 10 Dec 2020

Cited by 114 | Viewed by 21814

Abstract

Emerging technologies, such as smart wearable devices, augmented reality (AR)/virtual reality (VR) displays, and naked-eye 3D projection, have gradually entered our lives, accompanied by an urgent market demand for high-end display technologies. Ultra-high-resolution displays, flexible displays, and transparent displays are all important types of future display technology, and traditional display technology cannot meet the relevant requirements. Micro-light-emitting diodes (micro-LEDs), which have the advantages of a high contrast, a short response time, a wide color gamut, low power consumption, and a long life, are expected to replace traditional liquid-crystal displays (LCD) and organic light-emitting diodes (OLED) screens and become the leaders in the next generation of display technology. However, there are two major obstacles to moving micro-LEDs from the laboratory to the commercial market. One is improving the yield rate and reducing the cost of the mass transfer of micro-LEDs, and the other is realizing a full-color display using micro-LED chips. This review will outline the three main methods for applying current micro-LED full-color displays, red, green, and blue (RGB) three-color micro-LED transfer technology, color conversion technology, and single-chip multi-color growth technology, to summarize present-day micro-LED full-color display technologies and help guide the follow-up research. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display)

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33 pages, 9414 KiB

Open AccessReview

The Stability of Metal Halide Perovskite Nanocrystals—A Key Issue for the Application on Quantum-Dot-Based Micro Light-Emitting Diodes Display

by Zhibin Shangguan, Xi Zheng, Jing Zhang, Wansheng Lin, Weijie Guo, Cheng Li, Tingzhu Wu, Yue Lin and Zhong Chen

Nanomaterials 2020, 10(7), 1375; https://doi.org/10.3390/nano10071375 - 15 Jul 2020

Cited by 34 | Viewed by 6468

Abstract

The metal halide perovskite nanocrystal (MHP-NC), an easy-to-fabricate and low cost fluorescent material, is recognized to be among the promising candidates of the color conversion material in the micro light-emitting diode (micro-LED) display, providing that the stability can be further enhanced. It is found that the water steam, oxygen, thermal radiation and light irradiation—four typical external factors in the ambient environment related to micro-LED display—can gradually alter and destroy the crystal lattice. Despite the similar phenomena of photoluminescence quenching, the respective encroaching processes related to these four factors are found to be different from one another. The encroaching mechanisms are collected and introduced in separate categories with respect to each external factor. Thereafter, a combined effect of these four factors in an environment mimicking real working conditions of micro-LED display are also introduced. Finally, recent progress on the full-color application of MHP-NC is also reviewed in brief. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display)

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29 pages, 10264 KiB

Open AccessReview

Advances in Quantum-Dot-Based Displays

by Yu-Ming Huang, Konthoujam James Singh, An-Chen Liu, Chien-Chung Lin, Zhong Chen, Kai Wang, Yue Lin, Zhaojun Liu, Tingzhu Wu and Hao-Chung Kuo

Nanomaterials 2020, 10(7), 1327; https://doi.org/10.3390/nano10071327 - 06 Jul 2020

Cited by 73 | Viewed by 11325

Abstract

In terms of their use in displays, quantum dots (QDs) exhibit several advantages, including high illumination efficiency and color rendering, low-cost, and capacity for mass production. Furthermore, they are environmentally friendly. Excellent luminescence and charge transport properties of QDs led to their application in QD-based light-emitting diodes (LEDs), which have attracted considerable attention in display and solid-state lighting applications. In this review, we discuss the applications of QDs which are used on color conversion filter that exhibit high efficiency in white LEDs, full-color micro-LED devices, and liquid-type structure devices, among others. Furthermore, we discuss different QD printing processes and coating methods to achieve the full-color micro-LED. With the rise in popularity of wearable and see-through red, green, and blue (RGB) full-color displays, the flexible substrate is considered as a good potential candidate. The anisotropic conductive film method provides a small controllable linewidth of electrically conductive particles. Finally, we discuss the advanced application for flexible full-color and highly efficient QD micro-LEDs. The general conclusion of this study also involves the demand for a more straightforward QD deposition technique, whose breakthrough is expected. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display)

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