scholarly journals Improved Color Purity of Monolithic Full Color Micro-LEDs Using Distributed Bragg Reflector and Blue Light Absorption Material

Coatings ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 436 ◽  
Author(s):  
Shao-Yu Chu ◽  
Hung-Yu Wang ◽  
Ching-Ting Lee ◽  
Hsin-Ying Lee ◽  
Kai-Ling Laing ◽  
...  
Keyword(s):  
Blue Light ◽  
Light Absorption ◽  
Bragg Reflector ◽  
Color Purity ◽  
Distributed Bragg Reflector ◽  
Light Emitting ◽  
Full Color ◽  
Conversion Materials ◽  
Bottom Side ◽  
Color Conversion

In this study, CdSe/ZnS core-shell quantum dots (QDs) with various dimensions were used as the color conversion materials. QDs with dimensions of 3 nm and 5 nm were excited by gallium nitride (GaN)-based blue micro-light-emitting diodes (micro-LEDs) with a size of 30 μm × 30 μm to respectively form the green and red lights. The hybrid Bragg reflector (HBR) with high reflectivity at the regions of the blue, green, and red lights was fabricated on the bottom side of the micro-LEDs to reflect the downward light. This could enhance the intensity of the green and red lights for the green and red QDs/micro-LEDs to 11% and 10%. The distributed Bragg reflector (DBR) was fabricated on the QDs color conversion layers to reflect the non-absorbed blue light that was not absorbed by the QDs, which could increase the probability of the QDs excited by the reflected blue light. The blue light absorption material was deposited on the DBR to absorb the blue light that escaped from the DBR, which could enhance the color purity of the resulting green and red QDs/micro-LEDs to 90.9% and 90.3%, respectively.

scholarly journals Use of Recycling-Reflection Color-Purity Enhancement Film to Improve Color Purity of Full-Color Micro-LEDs

2022 ◽  
Vol 17 (1) ◽  
Author(s):  
Zhi Ting Ye ◽  
Jun-Yi Wu
Keyword(s):  
Conversion Efficiency ◽  
High Efficiency ◽  
Color Purity ◽  
Incident Wavelength ◽  
Excitation Light ◽  
Full Color ◽  
Conversion Materials ◽  
Pass Through ◽  
Color Conversion ◽  
Light Conversion Efficiency

Abstract A common full-color method involves combining micro-light-emitting diodes (LEDs) chips with color conversion materials such as quantum dots (QDs) to achieve full color. However, during color conversion between micro-LEDs and QDs, QDs cannot completely absorb incident wavelengths cause the emission wavelengths that including incident wavelengths and converted wavelength through QDs, which compromises color purity. The present paper proposes the use of a recycling-reflection color-purity-enhancement film (RCPEF) to reflect the incident wavelength multiple times and, consequently, prevent wavelength mixing after QDs conversion. This RCPEF only allows the light of a specific wavelength to pass through it, exciting blue light is reflected back to the red and green QDs layer. The prototype experiment indicated that with an excitation light source wavelength of 445.5 nm, the use of green QDs and RCPEFs increased color purity from 77.2% to 97.49% and light conversion efficiency by 1.97 times and the use of red QDs and RCPEFs increased color purity to 94.68% and light conversion efficiency by 1.46 times. Thus, high efficiency and color purity were achieved for micro-LEDs displays. Graphical Abstract

scholarly journals Device Modeling of Quantum Dot–Organic Light Emitting Diodes for High Green Color Purity

2021 ◽  
Vol 11 (6) ◽  
pp. 2828
Author(s):  
Byoung-Seong Jeong
Keyword(s):  
Quantum Dot ◽  
Emission Spectrum ◽  
Blue Light ◽  
Light Emitting Diodes ◽  
Organic Light Emitting Diodes ◽  
Color Purity ◽  
Wavelength Band ◽  
Light Emitting ◽  
Green Color ◽  
Organic Light

In this study, the optimal structure for obtaining high green color purity was investigated by modeling quantum dot (QD)–organic light-emitting diodes (OLED). It was found that even if the green quantum dot (G-QD) density in the G-QD layer was 30%, the full width at half maximum (FWHM) in the green wavelength band could be minimized to achieve a sharp emission spectrum, but it was difficult to completely block the blue light leakage with the G-QD layer alone. This blue light leakage problem was solved by stacking a green color filter (G-CF) layer on top of the G-QD layer. When G-CF thickness 5 μm was stacked, blue light leakage was blocked completely, and the FWHM of the emission spectrum in the green wavelength band was minimized, resulting in high green color purity. It is expected that the overall color gamut of QD-OLED can be improved by optimizing the device that shows such excellent green color purity.

scholarly journals Operando direct observation of spin-states and charge-trappings of blue light-emitting-diode materials in thin-film devices

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Fumiya Osawa ◽  
Kazuhiro Marumoto
Keyword(s):  
Blue Light ◽  
High Performance ◽  
Density Functional ◽  
Light Emitting Diode ◽  
Green Light ◽  
Spin States ◽  
Light Emitting ◽  
Full Color ◽  
Color Displays ◽  
Materials Used

Abstract Spin-states and charge-trappings in blue organic light-emitting diodes (OLEDs) are important issues for developing high-device-performance application such as full-color displays and white illumination. However, they have not yet been completely clarified because of the lack of a study from a microscopic viewpoint. Here, we report operando electron spin resonance (ESR) spectroscopy to investigate the spin-states and charge-trappings in organic semiconductor materials used for blue OLEDs such as a blue light-emitting material 1-bis(2-naphthyl)anthracene (ADN) using metal–insulator–semiconductor (MIS) diodes, hole or electron only devices, and blue OLEDs from the microscopic viewpoint. We have clarified spin-states of electrically accumulated holes and electrons and their charge-trappings in the MIS diodes at the molecular level by directly observing their electrically-induced ESR signals; the spin-states are well reproduced by density functional theory. In contrast to a green light-emitting material, the ADN radical anions largely accumulate in the film, which will cause the large degradation of the molecule and devices. The result will give deeper understanding of blue OLEDs and be useful for developing high-performance and durable devices.

AlGaInP Light Emitting Diode with Coupled Distributed Bragg Reflector Structure

2017 ◽  
Vol 54 (5) ◽  
pp. 052301
Author(s):  
郑元宇 Zheng Yuanyu ◽  
吴超瑜 Wu Chaoyu ◽  
林峰 Lin Feng ◽  
伍明跃 Wu Mingyue ◽  
周启伦 Zhou Qilun ◽  
...  
Keyword(s):  
Light Emitting Diode ◽  
Bragg Reflector ◽  
Distributed Bragg Reflector ◽  
Light Emitting
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