Breakthrough in Red Quantum LEDs: Engineers Achieve Record 31% Efficiency for Enhanced Display Color and Brightness

A team of researchers from the School of Engineering at The Hong Kong University of Science and Technology (HKUST) has made significant progress in the field of quantum rod light-emitting diodes (QR-LEDs), achieving record-high efficiency levels for red QR-LEDs. This breakthrough is expected to bring about significant advancements in next-generation display and lighting technologies, promising users of smartphones and televisions a more vibrant and enhanced visual experience. The findings have been published in the journal Advanced Materials.

Light-emitting diodes (LEDs) have been widely used in electronic devices for many years. Recent advancements in quantum materials have led to the development of quantum dot LEDs (QD-LEDs) and QR-LEDs. QD-LEDs offer superior color purity and brightness compared to traditional LEDs. However, the outcoupling efficiency has become a major challenge, limiting further improvements in performance.

Quantum rods, the basis of QR-LEDs, are elongated nanocrystals with unique optical properties that can be tailored to enhance light emission direction and improve outcoupling efficiency. Despite these advantages, QR-LEDs face challenges such as low photoluminescence quantum yield and leakage current due to poor thin-film quality.

To address these obstacles, a research team led by Prof. Abhishek K. Srivastava, Associate Professor of the Department of Electronic and Computer Engineering (ECE), focused on enhancing the optical performance of QR-LEDs through improved synthesis techniques. They achieved a remarkable photoluminescence quantum yield of up to 92% for both green and red quantum rods, along with uniform size distribution and shape confinement, crucial for optimizing QR-LED performance.

Past studies often overlooked carrier leakage caused by irregular quantum rod films and its impact on light coupling efficiency in QR-LEDs. To overcome this issue, the team developed an equivalent circuit model to illustrate the negative effects of leakage current in traditional QR-LED structures.

By strategically modifying the QR-LED device structure, the team achieved a dual breakthrough: enhancing balanced carrier injections and suppressing leakage current. As a result, the optimized red QR-LEDs reached a peak EQE of 31% and a peak brightness of 110,000 cd m⁻², setting a new standard in red QR-LED research. The team also applied their approach to green “dot-in-rod” quantum rods, achieving a peak EQE of 20.2% and an ultra-high luminance of 250,000 cd m⁻².

Prof. Srivastava emphasized the importance of their work in advancing the field of anisotropic nanocrystals and their commercial applications. He highlighted the fundamental advantages of quantum rods over quantum dots and the necessity of tailored solutions for elongated shaped nanocrystals like QR-LEDs.