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

Abstract

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.

Recent Progress in Micro‐LED‐Based Display Technologies

“…have reported the micro‐LED‐based RGB display using CdSe/ZnS QDs as color conversion materials and GaN‐based blue micro‐LEDs as excitation sources. [ 179 ] To improve the color contrast ratio, they confined each QD light using a black matrix (which have the property of nearly no transmission in the visible region) as shown in Figure a. The hybrid Bragg reflector (HBR) and DBR were deposited on the back and top side, respectively, to improve the reflection of light from the substrate side and also the color purity.…”

Prospects and challenges of mini‐LED, OLED, and micro‐LED displays

“…[123][124][125][126] However, some key issues remain to be solved, for example, blue light leakage would reduce the color purity of the display, the power conversion efficiency of the color conversion layer, and the ambient light excitation of the color conversion layer placed at top of the display panel. [127][128][129] When comparing different display technologies, three typical light source spectra for QD-LCD, OLED, and μLED are plotted in Figure 9. 117,130,131 Figure 10 shows their color gamut in Rec.2020 color space.…”

Doubling the optical efficiency of color‐converted micro‐light‐emitting diode displays with a patterned cholesteric liquid crystal polymer film

“…The blue LED array is protected and planarized by black photoresist to prevent lateral leakage of blue light. 11,12 The blue light emitted from the top passes through the adhesion layer and is down converted into green and red lights by the QD or perovskite material. Afterward, the leaked blue light is recycled by the patterned CLC to improve CCE.…”

“…It consists of a blue micro‐LED array at the bottom, an adhesion layer, a patterned color‐conversion film, a patterned CLC film, and a top CF array to form RGB subpixels. The blue LED array is protected and planarized by black photoresist to prevent lateral leakage of blue light 11,12 . The blue light emitted from the top passes through the adhesion layer and is down converted into green and red lights by the QD or perovskite material.…”