Researchers at the Hong Kong University of Science and Technology (HKUST) School of Engineering have cracked a major challenge in display technology by inventing the world's brightest and most energy efficient quantum rod LEDs (QRLEDs). These next-generation QRLEDs feature optimized deep green emission at the top of the colour triangle, enabling displays with unprecedented colour purity and a maximized colour gamut. Boasting a longer lifespan and triple the brightness of previous models, these cutting-edge light sources deliver energy-efficient, ultra-vivid visuals for smartphones, televisions, and AR/VR devices while further enhancing colour performance.
Light-emitting diodes (LEDs) have been widely used in electronic products for decades. Recent advancements in quantum materials have given rise to quantum dot LEDs (QLEDs) and QRLEDs. Both offer narrow emission bandwidths and high colour purity, surpassing traditional LEDs. Among these, QRLEDs excel with higher light outcoupling efficiency. However, QRLEDs face challenges: their green emission underperforms QLEDs due to inefficient charge injection, electron leakage at interfaces, and structural barriers like thick insulating shells and long organic ligands (molecules attached to surface of a nanorod) that hinder charge transport and stability.
To tackle these problems, the team led by Prof. Abhishek K. SRIVASTAVA, Associate Professor at the Department of Electronic and Computer Engineering, innovated a new class of green-emitting quantum rods featuring a customized core-gradient alloy structure with minimized outer shell thickness. This design achieves highly bright deep green emission (515 - 525 nm) at the peak of the colour triangle, maximizing display colour gamut. The team also engineered rods with uniform, smooth morphology and shorter length, enabling dense, void-free film packing. Further innovations include shorter organic ligands, a bilayer hole transport layer, collectively enhancing charge balance and suppressing electron leakage to boost efficiency and stability.
"We have successfully developed remarkably efficient and bright green-emitting QRLEDs by precisely designing the quantum rod composition, morphology, shape, and ligand structure, alongside the rational engineering of the device's hole transport layer," explained Prof. Srivastava, corresponding author of the paper.
This invention has achieved high performance in the following areas:
- Record Efficiency: Turning electricity into light more effectively than ever, with 24% external quantum efficiency (EQE) compared to older models' 22% EQE.
- Unmatched Brightness per Energy: Producing 89 cd A⁻¹ (candelas per ampere) a measure of brightness per unit of energy, outperforming all existing QRLEDs.
- Ultra-Bright Output: Shining 3× brighter than older green LEDs, achieving a peak luminance exceeding 500,000 cd m⁻².
- Longevity Leap: Demonstrated operational stability exceeding 22,000 hours, positioning the technology for commercial display applications.
"Our work demonstrates that meticulous control over nanorod composition and interface engineering can lead to disruptive advances in optoelectronic performance. This paves the way for high-resolution, energy-efficient displays with unprecedented brightness and longevity," said Prof. Srivastava.
Members of the research team are from the State Key Laboratory of Displays and Opto-Electronics, Center for Display Research, and the Department of Electronic and Computer Engineering, HKUST. The co-first authors are Postdoctoral Fellow Dr. Maksym PRODANOV and PhD candidate Kumar MALLEM. Their research paper, titled "Highly Efficient and Stable Green Quantum Rod LEDs Enabled by Material and Charge Injection Engineering", was recently published in the prestigious journal Advanced Materials.
