Development of next-generation perovskite LED source technology capable of implementing natural colors
A team led by Professor Im Sang-hyuk develops high-purity red, green, and blue quantum dots featuring a luminous line width of less than 20nm Published as a cover paper in Cell Reports Physical Science

▲ From left: Heo Jin-hyuck, research professor (Korea University, first author), Park Jin-kyoung, doctoral student (Korea University, first author), and Im Sang-hyuk, professor (Korea University, corresponding author)

The research team of Professor Im Sang-hyuk of the Department of Chemical and Biological Engineering at the College of Engineering developed the world's first high-purity red, green, and blue perovskite quantum dot synthesis technology featuring a line width of 20 nm or less to implement a next-generation perovskite LED capable of realizing natural colors. The research was published as a cover paper in the September 2nd (local time) issue of “Cell Reports Physical Science,” the sister magazine of Cell, a global international academic journal.

* Paper Title : Full color spectrum coverage by high colour-purity perovskite nanocrystal light emitting diodes
* Author Information: Heo Jin-hyuck, research professor (Korea University, first author), Park Jin-kyoung, doctoral student (Korea University, first author), Im Sang-hyuk, professor (Korea University, corresponding author)

The FPDs (Flat Panel Displays) used in smartphones and TVs are evolving from LCDs (Liquid Crystal Displays) to OLEDs (Organic Light Emitting Displays) and QLEDs (Quantum dot LEDs). However, their luminous line width is 30 nm or more, with the drawback that the color image viewed by the eye cannot be accurately implemented on the display. Therefore, to implement natural colors, the development of a new luminous body featuring a narrow luminous line width has been necessary.
* Perovskite: The crystal structure of minerals discovered by the Russian scientist, Lev Perovski

AMX3 (A = 1 cation, M = Pb, Sn, X = halogen) structure of metal halide crystal .
* LCD: liquid crystal display, OLED: organic light emitting display, QLED: quantum dot light emitting display

Perovskite, which is currently in the spotlight worldwide as a next-generation high-efficiency, low-cost solar cell, is known to emit very strong light like quantum dots when nano-crystallized. Unlike conventional chalcogen-based semiconductor quantum dots, perovskite is composed of ionic crystals and has a very high quantum efficiency due to low defect generation. It has a quantum well-structured crystal structure and a very narrow luminous line width. Due to these characteristics, many studies are being conducted into perovskite as a potential next-generation light emitter.

Such perovskite nanocrystal (quantum dot) light emitters are made through a high-temperature solution process, and the color control has been implemented through a substitution reaction by halogen anions. However, the non-uniformity of this substitution reaction has caused the line width of the emission spectrum to widen, resulting in poor color purity.

The team has developed a new synthesis method that allows the uniform substitution of halogenated anions at a relatively low reaction temperature by introducing halogen acid and does not leave impurities after the reaction. In this way, the team developed a perovskite nanocrystal light emitter of high-purity uniform composition lacking impurities.

The developed perovskite nanocrystal light emitter has a luminous spectrum line width of less than 20 nm in the entire visible light region, thus allowing the implementation of a high color purity perovskite LED capable of realizing natural colors.

Professor Im said, “We have verified the possibility that perovskite nanocrystalline light emitters can replace the color filters of displays and can be applied to the self-luminous LEDs currently in use to implement high color purity displays capable of realizing natural colors.”

This research was supported by the Ministry of Science and ICT, the National Research Foundation of Korea's Leading Research Center (ERC, Functional Crystallization Center) and the Nanomaterial Source Technology Development Project.



[ Figure Description ]

▲Figure 1. Transmission electron micrograph of perovskite nanocrystal light emitter (top left),

emission spectrum (top right), and photograph of luminescence under UV irradiation (bottom).

▲ Figure 2. Low temperature emission spectrum. Existing synthesis method (left), new synthesis method (right).

▲ Figure 3. Electroluminescence (EL) device emission spectrum (left), CIE coordinates (right).