Perovskites are materials with excellent ability to mutually convert light and electricity, and are attracting attention not only as next-generation solar cells but also as next-generation display materials that could surpass existing organic light-emitting diodes (OLEDs) and quantum dot light-emitting diodes (QLEDs). A domestic research team has developed a method to mass-produce high-quality perovskite nanocrystals for display applications.

On the 19th, the Ministry of Science and ICT announced that a research team led by Professor Tae-Woo Lee of the Department of Materials Science and Engineering at Seoul National University has developed a new perovskite nanocrystal synthesis technology. The research results were published in the international journal Nature on the 18th (local time). The goal is to commercialize the developed technology within one year.

● Defect control through low-temperature processing

Perovskite displays offer higher color representation than existing technologies and are advantageous for reducing the size of pixels, the minimum units that make up a screen. This makes them suitable for virtual reality (VR) devices and wearable equipment, which must implement ultra-small pixels in close proximity to the eyes. The manufacturing process and raw materials are also assessed as relatively low-cost.

To implement perovskite displays, an efficient nanocrystal synthesis process is required. Previously, the mainstream approach was “hot injection,” which involves injecting materials into a high-temperature solution above 150 degrees Celsius; however, this method carries safety risks and requires special equipment that blocks oxygen and moisture, resulting in high costs. Technologies capable of synthesis at room temperature have also been proposed, but they have limitations in that productivity and quality drop sharply in mass production.

Focusing on the fact that rapid synthesis speed leads to defects and reduced uniformity, the research team developed a “low-temperature injection” synthesis method. The process involves injecting a solution of materials that form perovskite into a ligand solution cooled to around 0 degrees Celsius to create a quasi-emulsified state, followed by synthesis. Ligands are substances that control crystal growth.

The low-temperature injection method effectively controls the speed of crystal synthesis and suppresses defect formation. The team succeeded in producing high-quality pure green perovskite emitters with a luminous efficiency of 100%.

As space and deep-sea exploration have recently become more active, demand has been increasing for displays that can be used in extreme environments. OLEDs, which use organic materials, have difficulty emitting light in low-temperature environments. Professor Lee stated, “When implemented at a low temperature of minus 40 degrees Celsius, perovskite exhibits increased efficiency and lifetime,” adding, “It is expected to have differentiation from other displays in cold regions such as polar areas or the deep sea.”

This achievement has high industrial value because it is based on a fundamental patent secured by the research team in 2014. This means that if perovskite displays are fully commercialized in the future, Korea could secure competitiveness.

In fact, the research team worked with S&Display, a faculty startup company, to produce a perovskite nanocrystal-based color conversion film, mount it on a tablet display, and verify its commercialization potential.

● Three consecutive world-class display research achievements

Professor Lee’s team also published display research results last month in both Nature and Science, which are regarded as the most prestigious journals in the scientific community. This means the team has produced three excellent achievements in just one month.

The results published in Science reported the development of a “hierarchical shell” technology that improves the efficiency and lifetime of perovskite nanocrystals by compensating for structural defects. The results published in Nature reported the development of stretchable OLED devices that use MXene-based electrodes, a two-dimensional new material, and maintain performance and brightness even when stretched 1.6 times their original length.

In particular, the study published in Science, which was selected as a cover paper, presented the potential of perovskite devices. Quantum dots used in QLEDs typically adopt a structure in which they are encapsulated with a shell to extend lifetime. Perovskite devices already exhibit theoretically superior performance to quantum dots even without a shell structure, indicating room to further extend their lifetime.

Professor Lee emphasizes the importance of viewing science from a humanities perspective. He argues that researchers must feel their own field is important in order to achieve accomplishments over a long period of time.

He stated, “These achievements were possible because students and researchers trusted me,” adding, “I believe it is thanks to the bonds with students and the culture of the laboratory.”

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