Korean researchers have developed a technology that can dramatically improve the performance of quantum dot light emitting diodes (QLEDs), which have become a popular candidate for next-generation display devices, following organic light emitting diodes (OLEDs). Once the technology is successfully commercialized, it is expected to be widely used in a variety of display fields such as an ultra-high resolution display for augmented reality (AR) and virtual reality (VR), near eye display, and implantable photic stimulus light source.
The Electronics and Telecommunication Research Institute (ETRI) said on April 16 that it has developed a technology that improves the brightness, current and power efficiency of QLEDs by changing the molecular sieve constituting the surface of the quantum dot.
QLED is a display that uses quantum dots, which are light-emitting semiconductor particles. While OLEDs use organic materials, QLEDs use organic quantum dots. QLED has attracted industry’s attention because it is a display technology that reproduces natural colors by providing a wider color gamut than other devices.
However, QLED is not without its technical difficulties, the toughest one being the electron and hole transport imbalance in the light emitting layer. Electrons and holes injected into both electrodes meet at the quantum dots to emit light, and while electrons move up and down easily, holes are difficult to transport because of the slow transfer between the electrodes and the quantum dot energy. As a result, QLED performance deteriorates, shortening the life of the element.
The research team resolved the electron and hole mobility imbalance by placing a quantum dot on the emissive layer in the display and replacing the portion of the hole with a material called pyridine. Pyridine moves holes faster, reducing the distance between the quantum dots and the hole transport layer, and form an intermediate energy layer. The newly formed intermediate energy layer serves to enhance the efficiency of light emission by the electrons and hole.
In addition, the team made changes to move holes and electrons smoothly without additional voltage so that they emit light at lower voltages. The hole moves faster and meets a lot of electrons with high mobility, which leads to emission of bright light without application of additional voltage.
The researchers explained that using the technology, they succeeded in producing a QLED of up to 4.5 times brighter, 1.7 times higher current efficiency and 2.3 times higher power efficiency than conventional elements. In particular, it can be applied equally to all the color quantum dots including red, green, and blue (R, G, B), which is expected to be helpful in commercialization of QLEDs in the future.
Lee Hyun-koo, director of ETRI's flexible element research group, said, "The newly developed QLED has a color reproduction rate of 159 percent, which allows us to implement colors closer to natural colors, and it can beused for various applications, like the next generation displays. We plan to carry out further studies with the aim of applying QLED to micro-displays in the future.”
The results of the study were published as a cover article in international journal Chemistry of Materials (March issue).