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Microarray Formation Maximizes Quantum Dot Color Conversion

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To enhance the color conversion process of quantum dots for use in LEDs, micro-LEDS, near-field displays, and other devices, researchers from Beijing Institute of Technology have developed perovskite quantum dot (PQD) microarrays. The assembly strategy aims to overcome a common problem facing conventional quantum dot color conversion (QDCC) pixels that are fabricated by inkjet printing: the thinness of the pixels preventing the dots from achieving efficient color conversion.

QDCC is a foundational technology in the design of full-color light-emitting devices, due to the ability of the technique to improve color performance. It additionally provides a wide range of color performance and easy integration. In printing, it can be used to achieve full-color OLEDs and micro-LEDs.

However, the conventional combination of quantum dots and coffee-ring effects, or puddle of particle-laden liquid that occur after evaporation, lowers the light conversion efficiency and emission uniformity in quantum dot microarrays. This also contributes to blue-light leakage or optical crosstalk, where unwanted coupling occurs between signal paths.

A research team has developed perovskite quantum dots microarrays with strong potential for QDCC applications, including photonics integration, micro-LEDs, and near-field displays. Courtesy of Nano Research, Tsinghua University Press.
A research team has developed perovskite quantum dots microarrays with strong potential for QDCC applications, including photonics integration, micro-LEDs, and near-field displays. Courtesy of Nano Research, Tsinghua University Press.
PQDs hold potential as an attractive material and can resolve some of the problems found in conventional QDCC, according to the researchers. While perovskite quantum dots are a relatively new technology, they have already been shown to be suitable for electronic and optoelectronic applications. By using patterned black photoresist molds to make QD pixels, researchers increased pixel thickness to avoid optical crosstalk to achieve better printing results.

“To solve these problems, we fabricated 3D perovskite quantum dots microarrays by combining the inkjet printing and in situ fabrication of perovskite quantum dots during the photopolymerization of precursor ink,” said Gaoling Yang, an assistant professor in the School of Optics and Photonics at Beijing Institute of Technology. Inkjet printing features noncontact, material-efficient, and reproducible processing. As a result, it has attracted attention in patterned microarrays.

Using photopolymerization, the researchers achieved a PQD color conversion microarray with a pixel size of 20 μm. The fabricated microarrays achieved strong and uniform photoluminescence in large area because of the seamless integration with in situ-fabricated PQDs. The researchers’ technique demonstrated the potential use of the in situ direct print photopolymerization method for fabricating patterned multicolor PQD microarrays with a wide color gamut and high resolution.

Additionally, the PQD microarrays exhibit characteristics that are desirable for QDCC applications including 3D morphology, the researchers said.

The research was funded by the National Key Research and Development Program of China, the National Natural Science Foundation of China, and the Beijing Institute of Technology Fund Program for Young Scholars Research.

The research was published in Nano Research (www.doi.org/10.1007/s12274-022-4466-4).

Photonics Handbook
GLOSSARY
color
The attribute of visual experience that can be described as having quantitatively specifiable dimensions of hue, saturation, and brightness or lightness. The visual experience, not including aspects of extent (e.g., size, shape, texture, etc.) and duration (e.g., movement, flicker, etc.).
quantum dots
Also known as QDs. Nanocrystals of semiconductor materials that fluoresce when excited by external light sources, primarily in narrow visible and near-infrared regions; they are commonly used as alternatives to organic dyes.
optoelectronics
A sub-field of photonics that pertains to an electronic device that responds to optical power, emits or modifies optical radiation, or utilizes optical radiation for its internal operation. Any device that functions as an electrical-to-optical or optical-to-electrical transducer. Electro-optic often is used erroneously as a synonym.
photopolymerization
A process in which a mixture of one or more monomers, plus a catalyst, polymerize under exposure to light radiation. Photopolymerization permits a hologram to be exposed, fixed and reconstructed in about one-half second.
Displayscolorquantum dotsLEDsOLEDsmicroLEDsnear fieldinkjet printingAsia PacificResearch & TechnologyeducationBeijing Institute of Technology optical crosstalkoptoelectronicsmicroarraysmaterialsphotopolymerizationcolor conversionperovskiteperovskite quantum dotsphotoluminescence

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