On November 4th, the Hong Kong University of Science and Technology announced that a research team led by the university's School of Engineering has recently made significant progress in quantum rod light-emitting diode (QR-LED) technology, successfully achieving a record-breaking high efficiency level for red QR-LEDs. This breakthrough is expected to reshape next-generation display and lighting technologies, bringing more vivid and higher-quality visual experiences to devices such as smartphones and televisions.
The team developed a red QR-LED with a light extraction efficiency of up to 31% (Image source: Hong Kong University of Science and Technology).
It is understood that with the rise of quantum materials, quantum dot LEDs (QD-LEDs) and quantum rod LEDs (QR-LEDs) have emerged. Compared with traditional LEDs, QD-LEDs have higher color purity and brightness, but light extraction efficiency remains a key bottleneck limiting the improvement of their external quantum efficiency (EQE).
QR-LEDs utilize elongated nanocrystals—quantum rods—which possess unique optical properties. Through structural design optimization, the light emission direction can be improved, enhancing light extraction efficiency. However, further development of QR-LEDs is limited by two major challenges: firstly, the photoluminescence quantum yield is relatively low; and secondly, insufficient thin-film quality easily leads to leakage current.
To overcome bottlenecks, a research team led by Associate Professor Abhishek K. Srivastava of the Department of Electrical and Computer Engineering at HKUST has significantly improved the optical performance of QR-LEDs through a precise synthesis process. The team successfully fabricated red and green quantum rods with uniform size and shape, significantly increasing the photoluminescence quantum yield to 92%, laying a solid foundation for performance optimization.
The research team also addressed the previously overlooked leakage current issue by establishing an equivalent circuit model and conducting an in-depth analysis of the current leakage mechanism in traditional QR-LED structures. By improving the device structure, the team effectively suppressed leakage current while enhancing carrier injection efficiency, significantly improving the overall device performance.
With the adoption of the new technology, the optimized red QR-LED achieved an external quantum efficiency of up to 31% and a brightness of 110,000 cd/m², setting a new record in the field of red QR-LEDs. To verify the versatility of the technology, the team applied the same method to green quantum rod devices, achieving equally excellent results: an external quantum efficiency of 20.2% and a brightness of 250,000 cd/m². This achievement not only demonstrates the effectiveness of the innovative method but also showcases its broad application potential in quantum rods of different colors and structures.
Professor Srivastava pointed out that previous research has focused on QD-LED structure optimization, but these techniques are not applicable to elongated quantum rods. Through microstructural analysis, the team discovered that numerous pinholes exist in the QR-LED thin film, which is the main cause of current leakage. By redesigning the device structure, the team successfully improved the quality of the emitting layer, completely solving the leakage problem and injecting new impetus into the further research and commercial application of anisotropic light-emitting nanocrystals.
The research findings have been published in the top international academic journal *Advanced Materials*, with the paper titled "Inverted Device Engineering for Efficient and Bright Quantum Rod LEDs". The research team comprised members from the State Key Laboratory of Display and Optoelectronic Technology, the Display Technology Research Center, the Department of Electronic and Computer Engineering, and the Department of Physics at the Hong Kong University of Science and Technology (HKUST), in collaboration with the University of Edinburgh. The first author of the paper is Liao Zebing, a doctoral student in the Department of Electronic and Computer Engineering, and the research was conducted under the guidance of Professor Srivastava. (Source: Hong Kong University of Science and Technology)
