White light-emitting diodes (LEDs) with excellent color saturation and extended lives have been developed by scientists over the years for use in flexible lighting and display technologies. Due to their ability to adjust color, flexibility, high quantum efficiency, narrow-spectrum emission, and superior photoluminescence, colloidal quantum dots (QDs) are strong contenders for the next generation of illumination technologies. They may eventually replace organic LED (OLED) and liquid crystal displays (LCD).
Rare Earth Elements Color Conversion Materials
Quantum dots' advanced properties might enable micro-LED displays with smaller pixels.
Widely employed in planar and lighting illuminator applications, white-light-emitting materials generally utilize phosphors containing rare earth elements (REEs) as their color conversion component. However, the existing approach is not sustainable due to the adverse effects of mining and using rare earth elements on the economy and environment.
Developing REE-free color conversion materials with high flexibility, stability and efficiency has been a leading research topic. Flexible lights and displays have been made using thin, flexible, self-emitting OLED materials in recent years, but their dependability and challenges with low driving currents are troublesome. Recent research has improved QD technologies' efficiency, reliability, and color-tunability.
Chip Designs Suggested by Previous Researchers
Some researchers have suggested blue or UV chip designs with colloidal quantum dot sheets as flexible planar light-source modules since portable consumer electronics need lighting components to be flexible, thin and lightweight. Wide-color-gamut display backlights can be a good fit for hybrid-type LEDs based on perovskite quantum dots (PQDs).
White LEDs with quantum dot color converters and mixed perovskite quantum dots, including high-stability mesoporous silica nanocomposites with a broad color range, have been employed as backlights for display applications. Drive-current algorithms have been used in mini-LED displays to increase the color gamut and high dynamic range.
Fabricating and Packaging Wide-Angle (WA) Mini-Light-Emitting Diode (Mini-LED) Devices
In this study, the researchers proposed a packaging technique for WA mini-LEDs with a QD film producing a flexible, ultrathin, planer light source that can serve as a backlight for portable QLED displays while significantly reducing the number of LEDs needed for the same area compared to the previous packaging specifications.
Packaged Wide-Angle Mini-LEDs fabrication
GaN flip-chip blue LEDs with 450 nm emission wavelength were the foundation for wide-angle mini-LED chips. These chips' height, width, and length were 150, 127, and 228.6 μm, respectively. The benefits of the GaN flip-chip blue LEDs include packaging with lower thermal resistance, without the need for a lead frame, the capacity to tolerate high current densities, and without wire bonding.
There were six main steps of the packaging process, including diffusion layer film paste on the substrate, light guide film paste on the substrate, microchip dye bonding, molding side wall, cutting and separation from glass.
Dimensions of the finished square wide-angle mini-LED package were 800 x 800 x 580 µm3. This approach not only significantly reduces the number of light sources utilized but also creates light sources that are very thin, flexible and effective. These results suggest that the wide-angle mini-LED square packages designed with these techniques provide good backlights for cutting-edge QLED display applications.
Quantum Dot Film Fabrication
A hybrid quantum dot film was created by combining commercial red and green quantum dots with a UV-polymer. Using an automated blade coater, the hybrid layers were coated on polyethylene terephthalate (PET) films as covering layers to create sandwich-like structures. After that, the PET/QD-PMMA/PET film was laminated and exposed to 365 nm UV light for 30 seconds to cure it. To create an ODL/PET/QD-PMMA/PET/ODL film, the optical diffusion layer (ODL) was coated onto the PET/QD-PMMA/PET film using a doctor-blade coater.
Fabricating Flexible Circuit Board
A circuit board was created using epoxy glass fiber arrayed with 3200 packed WA mini-LEDs. The backlight unit's construction comprised WA mini-LEDs covered with QD, prism, and optical films. When these characteristics came together, an ultrathin, flat, and homogeneous light source was created. The optical films were layered one on top of the other with little space between them.
The WA mini-LEDs' performance was greatly enhanced using a unique packaging method. The center intensity decreased to 26.5 percent, and the light extraction efficiency increased to 96.1 percent compared to simple mini-LEDs. Compared to unpackaged mini-LEDs with the same surface area, this led to a wider emission angle, a more extensive lighting area, and fewer LEDs. These findings, together with the high color gamut of 104.2 percent, show that future QLED displays may use this backlight-unit technology and achieve a wide color range.
Yen-Lung Chen, Wen-Chung Chin, Chun-Wei Tsai, Chang-Che Chiu, Ching-Ho Tien, Zhi-Ting Ye, and Pin Han (2022) Wide-Angle Mini-Light-Emitting Diodes without Optical Lens for an Ultrathin Flexible Light Source. Micromachines. https://www.mdpi.com/2072-666X/13/8/1326/htm