Browsing by Author "Liu, Zhaojun"

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Advances in Quantum-Dot-Based Displays
(2020-07-01)
Huang, Yu-Ming
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Singh, Konthoujam James
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Liu, An-Chen
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Lin, Chien-Chung
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Chen, Zhong
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.
Alternative Strategy to Reduce Surface Recombination for InGaN/GaN Micro-light-Emitting Diodes-Thinning the Quantum Barriers to Manage the Current Spreading
(2020-08-06)
Chang, Le
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Yeh, Yen-Wei
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Hang, Sheng
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Tian, Kangkai
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Kou, Jianquan
Owing to high surface-to-volume ratio, InGaN-based micro-light-emitting diodes (mu LEDs) strongly suffer from surface recombination that is induced by sidewall defects. Moreover, as the chip size decreases, the current spreading will be correspondingly enhanced, which therefore further limits the carrier injection and the external quantum efficiency (EQE). In this work, we suggest reducing the nonradiative recombination rate at sidewall defects by managing the current spreading effect. For that purpose, we properly reduce the vertical resistivity by decreasing the quantum barrier thickness so that the current is less horizontally spreaded to sidewall defects. As a result, much fewer carriers are consumed in the way of surface nonradiative recombination. Our calculated results demonstrate that the suppressed surface nonradiative recombination can better favor the hole injection efficiency. We also fabricate the mu LEDs that are grown on Si substrates, and the measured results are consistent with the numerical calculations, such that the EQE for the proposed mu LEDs with properly thin quantum barriers can be enhanced, thanks to the less current spreading effect and the decreased surface nonradiative recombination.
Color Difference and Thermal Stability of Flexible Transparent InGaN/GaN Multiple Quantum Wells Mini-LED Arrays
(2020-07-01)
Lu, Bo
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Wang, Yan
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Hyun, Byung-Ryool
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Kuo, Hao-Chung
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Liu, Zhaojun
We present studies of the color uniformity and thermal stability of a flexible and transparent 32 x 32 mini-LED array on polyethylene terephthalate (PET) substrate up to a brightness rating of 5000 nits at room temperature, whose brightness is required for outdoor display applications. Surprisingly, even at 5000 nits, the temperature variation on the surface of the LED array is less than 9 degrees C, despite the relatively low thermal diffusivity of the polymer substrates. The average surface temperature was 33 degrees C. This indicates that the heat dissipation of the fabricated LED array is superior with even a polymer substrate. Further, the narrow electroluminescent (EL) emissions from the mini-LED array help to realize wider color gamut than Rec. 2020 color gamut in display applications. The color differences from the EL spectra were calculated at three different brightness. The calculated values are far less than the color discrimination threshold of the human eye corresponding to 0.005 at all testing brightness and meet the display industry requirement for color difference.
Micro-light-emitting diodes with quantum dots in display technology
(2020-05-11)
Liu, Zhaojun
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Lin, Chun-Ho
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Hyun, Byung-Ryool
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Sher, Chin-Wei
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Lv, Zhijian
Micro-light-emitting diodes (mu-LEDs) are regarded as the cornerstone of next-generation display technology to meet the personalised demands of advanced applications, such as mobile phones, wearable watches, virtual/augmented reality, micro-projectors and ultrahigh-definition TVs. However, as the LED chip size shrinks to below 20 mu m, conventional phosphor colour conversion cannot present sufficient luminance and yield to support high-resolution displays due to the low absorption cross-section. The emergence of quantum dot (QD) materials is expected to fill this gap due to their remarkable photoluminescence, narrow bandwidth emission, colour tuneability, high quantum yield and nanoscale size, providing a powerful full-colour solution for mu-LED displays. Here, we comprehensively review the latest progress concerning the implementation of mu-LEDs and QDs in display technology, including mu-LED design and fabrication, large-scale mu-LED transfer and QD full-colour strategy. Outlooks on QD stability, patterning and deposition and challenges of mu-LED displays are also provided. Finally, we discuss the advanced applications of QD-based mu-LED displays, showing the bright future of this technology. Micro-LEDs: A fine display by quantum dots Micrometre-sized light-emitting diodes (LEDs) based on quantum dots (QDs) will propel the next generation of display technologies, a review by leading researchers shows. Conventional LED designs, with phosphor coatings that convert light to different colours, are difficult to make smaller than 20 micrometres. Jr-Hau He at City University of Hong Kong and co-workers explain how this problem can be tackled using QDs, tiny particles whose optical properties can be tuned by varying their size, providing brighter and more precise colours. Ultra-high-resolution displays based on phospholuminescent QD-LEDs are now being released to the market thanks to finely-controlled methods for synthesising QDs and depositing them onto films. Further research should focus on the best ways to stabilise and protect QD films within LEDs, and to continue developing electroluminescent QD-LEDs, which could potentially outperform their phospholuminescent cousins.