| Resolving electron-hole imbalance using quantum dot surface substitution technology
| 4.5 times brighter, 1.7 times more current efficient, 2.3 times more power efficient
| Improving QLED Efficiency by Changing Quantum Dot Surface Molecular Sieve
The Electronics and Telecommunications Research Institute (ETRI) announced on the 16th that it has successfully developed a technology that dramatically improves the performance of quantum dot light-emitting diodes (QLEDs), a next-generation display element.

QLED is a display technology that uses quantum dots, which are semiconductor particles that emit light on their own. While OLED has used organic materials, QLED uses semiconductors, i.e. quantum dots, instead of organic materials.

Recently, as demand for displays that reproduce colors closer to nature has increased, interest in QLED technology, which provides the widest color gamut, is also increasing.
ETRI has developed a core technology that can improve the brightness, current, and power efficiency of QLEDs by changing the molecular sieve that makes up the quantum dot surface through the development of QLED hole injection improvement technology.

The biggest challenge in QLED technology is the imbalance of electron-hole movement within the light-emitting layer.

The components that make up a QLED display emit light when electrons and holes injected from two electrodes meet at a quantum dot. While electrons move freely up and down, holes struggle to move due to slow energy transfer between the electrodes and the quantum dot. This electron-hole imbalance problem reduces the performance of quantum dot light-emitting diodes and shortens their lifespan, requiring research to address it.
The research team solved the imbalance problem by placing quantum dots on top of the display's brightly glowing emissive layer and replacing only the hole-carrying portion with a substance called pyridine. Using pyridine reduces the distance between the quantum dots and the hole-transport layer, creating an intermediate energy layer. This intermediate energy layer facilitates hole transport, increasing the efficiency with which electrons and holes meet to emit light. This is because light can only be emitted when electrons and holes coexist in a single layer.

Previously, only electrons could move smoothly, while holes could not follow. Furthermore, injecting additional holes required additional voltage. However, the research team has now enabled free and smooth movement of holes without the need for additional voltage, resulting in light emission even at low voltages. Even though the voltage is the same as OLED, the holes move faster and meet many fast-moving electrons, so they shine brightly.
As a result, it became possible to implement quantum dot light-emitting diodes with up to 4.5 times the brightness, 1.7 times the current efficiency, and 2.3 times the power efficiency compared to existing devices. Additionally, the research team reports that this technology can be applied equally to quantum dots of all colors—red, green, and blue (RGB)—and will be of great help in the future commercialization of QLEDs.
The technology developed by the research team was selected as the March cover paper of the Journal of Materials Chemistry, a leading international academic journal in the field of materials.

ETRI's Lee Hyeon-gu, head of the Flexible Device Research Group, said, "We plan to apply this technology to microdisplays that our research team is currently developing in the future," and added, "It shows a color reproducibility of approximately 159% of the US National Television System Committee (NTSC) standard, so it can express colors closer to natural colors, and it is expected to be applied in various ways to next-generation displays."
In this way, this technology can be utilized in various industries, such as ultra-high-resolution displays (HMDs) for augmented reality (AR) and virtual reality (VR), near-eye displays, and implantable optical stimulation light sources for biological stimulation/inhibition.

Meanwhile, this research was conducted as part of ETRI's core project, "Implantable Front-End Technology Development." The research team has completed 15 research papers and registered 15 patents for next-generation display research and development.