A domestic research team has developed an ultra-high-brightness red QLED through a multifaceted approach to quantum dot materials and device structures that can withstand high currents, and the diverse applications of self-luminous QLEDs are expected to expand beyond displays.

Seoul National University College of Engineering (Dean Byung-Ho Lee) announced on the 16th that a joint research team led by Professor Jeong-Hoon Kwak of the Department of Electrical and Computer Engineering and Professor Jae-Hoon Lim of Sungkyunkwan University (first authors Tae-Soo Lee and Byung-Jae Kim) developed a quantum dot material and device structure that can operate stably even under high-brightness conditions, as well as an ultra-high-brightness red QLED that emits up to 3.3 million nits of light and operates stably even under high-brightness operating states of tens of thousands of nits.

Currently, the use of self-luminous QLED is limited to mid- to low-brightness displays (hundreds to thousands of nits) such as TVs, laptops, and mobile phones. In order for QLED to be used in various fields such as AR/VR devices, outdoor displays, and even lighting and light therapy devices, high brightness conditions of tens of thousands of nits or more are required, but the QLED devices up to now have not operated at high brightness or have shown very low device efficiency and stability.

To achieve high brightness, a high current must be applied to the QLED. However, the Joule heat generated by the high current accelerates the deterioration of the device, and the luminescence efficiency of the quantum dot decreases due to the increase in non-luminescent Auger recombination caused by the generation of multiple excitons, making it difficult to produce high-brightness QLEDs.

The joint research team developed a material that can maintain luminescence efficiency even at high currents by effectively suppressing non-luminescent Auger recombination that occurs at high currents by precisely controlling the structure of the shell that makes up the quantum dot.

In addition, by using a silicon substrate with high thermal conductivity, the deterioration of the device due to heat was suppressed, and the brightness was increased by optimizing the top-emitting structure that increases the light extraction efficiency. Finally, by controlling the number of quantum dots inside the emitting layer, the formation of multi-exciton with low luminescence efficiency was minimized.

The QLED, manufactured through a multifaceted approach from materials to components, exhibits a maximum brightness of 3.3 million nits (light output of 50 mW), a current efficiency of 75.6 cd/A, and an expected half-life at an initial brightness of 100 nits, a whopping 125 million hours (approximately 14,269 years). This is the highest brightness, efficiency, and lifespan among QLEDs announced so far.

The results of this study are expected to contribute to the practical application of QLED displays and to be applicable to AR/VR devices and outdoor displays that require high brightness. In addition, the scope of application of self-luminous QLED is expected to expand beyond displays to lighting, lasers, and photobiomodulation therapy, allowing it to be applied to various light-related industries.

Meanwhile, the results of this study were published online on October 27 in the journal Advanced Materials, one of the most prestigious journals in the fields of materials, nanotechnology, and science, and were conducted with the support of the Ministry of Trade, Industry and Energy's Technology Innovation Project, Seoul National University's Creative Leading Young Researcher Project, and the Ministry of Science, ICT and Future Planning.