China is making significant strides in next-generation lighting technology, particularly with advancements in perovskite light-emitting diodes (LEDs). Recent research has focused on enhancing the stability and lifespan of these LEDs, paving the way for their widespread commercial application.
The Promise of Perovskite LEDs
Perovskite LEDs (PeLEDs) represent a new frontier in lighting and display technology. They combine the flexibility and thinness of organic LEDs (OLEDs) with the color tunability of traditional LEDs, offering potential advantages in terms of cost, efficiency, and performance. Metal halide perovskites, in particular, have emerged as promising materials for LEDs due to their unique physical properties and ease of manufacturing compared to conventional LEDs.
Key advantages of perovskite materials for LED applications include:
- High luminous efficiency: Perovskites exhibit high light-emission efficiency, making them suitable for energy-saving lighting solutions.
- Low cost: Perovskite materials are relatively inexpensive to synthesize, potentially leading to lower production costs compared to traditional LEDs.
- Processing flexibility: Perovskites can be deposited onto various flexible or rigid substrates, allowing for diverse application possibilities.
- Color tunability: The optical bandgap of perovskites can be tuned across the visible spectrum, enabling the creation of LEDs with different colors.
Overcoming the Stability Challenge
Despite their potential, perovskite LEDs have faced a major hurdle: instability, resulting in a short lifespan. Traditional PeLEDs often degrade rapidly, limiting their practical use. However, recent research in China has made significant breakthroughs in addressing this issue.
Innovative Strategies for Enhanced Stability
Chinese researchers have developed several innovative strategies to improve the stability of perovskite LEDs:
- Weakly Space-Confined Perovskite Films: A team from the University of Science and Technology of China (USTC), Fudan University, and Nanjing Tech University developed an alternative strategy based on weakly space-confined, large-grain crystals of all-inorganic perovskite to prepare perovskite films with larger crystalline grains and higher temperature resistance. This approach allows for larger crystals and higher temperature resistance, enhancing the LED’s durability.
- Novel Material Design: Researchers from USTC have identified and targeted the root cause of efficiency loss at high brightness by introducing a novel material design. This design has enabled record-breaking device performance.
- Stress Manipulation of Epitaxial Heterojunction Interface: To address phase instability in pure red CsPbI3 perovskite quantum dots, researchers have used a “stress manipulation of epitaxial heterojunction interface” strategy. This method allows for large-area in-situ controllable preparation of perovskite van der Waals (vdW) epitaxial heterojunctions, resulting in a high-efficiency, stable pure red perovskite LED.
- Lithium Halide Passivation: Studies have shown that lithium halides can efficiently passivate defects of halide vacancies, reduce trap state density, and suppress ion migration in perovskite films. This leads to improved efficiency and stability in green, blue, and red perovskite LEDs.
- Dual Defect Passivation: Researchers have explored the use of poly(ethylene glycol)diacrylate to passivate surface defects in perovskite films through additive doping and post-treatment strategies, enhancing the efficiency and stability of blue 3D perovskite LEDs.
- Crystal Engineering: A team from USTC has developed a novel approach to fabricating all-inorganic perovskite films featuring larger crystal grains and enhanced heat resistance. This method involves adding specific compounds into the perovskite material and employing a high-temperature annealing process, resulting in a new type of perovskite film with fewer defects and a more ordered internal structure.
Record-Breaking Performance
These innovative strategies have led to significant improvements in perovskite LED performance:
- Extended Lifespan: Researchers have extended the lifespan of PeLEDs to over 20 years at a brightness comparable to commercial displays. At 100 nits, which meets the standard for some commercial LED products, the new PeLEDs have a theoretical lifespan of more than 185,000 hours, or around 21 years.
- Increased Brightness: The brightness of perovskite LEDs has been increased to over 1.16 million nits, far exceeding the brightest commercial display screens, which typically cap out at several thousand nits.
- High External Quantum Efficiency: Researchers have achieved a peak external quantum efficiency of 24.2% and a maximum luminance of 24,600 cd m-2 in pure-red PeLEDs.
- Improved Luminous Efficiency: The luminous efficiency of new perovskite LEDs has reached over 22 percent, on par with commercial display products.
Miniaturization Advances
In addition to improving stability and performance, researchers are also making strides in perovskite LED miniaturization. A research team from Zhejiang University and the University of Cambridge has reported the downscaling of LEDs based on perovskite semiconductors to below conventional size limits.
Micro- and Nano-Perovskite LEDs
The team demonstrated micro- and nano-perovskite LEDs (micro-PeLEDs/nano-PeLEDs) with characteristic pixel lengths from hundreds of micrometers down to about 90 nm. This was achieved through a localized contact fabrication scheme that prevents non-radiative losses at the pixel boundaries.
Key achievements in perovskite LED miniaturization include:
- High External Quantum Efficiencies: Average external quantum efficiencies (EQEs) were maintained at around 20% across a wide range of pixel lengths (650 to 3.5 μm) for near-infrared (NIR) and green micro-PeLEDs.
- Record-High Pixel Density: The nano-PeLEDs with characteristic pixel lengths down to about 90 nm represent the smallest LEDs reported, enabling a record-high pixel density of 127,000 pixels per inch (PPI) among all classes of LED arrays.
These advancements in miniaturization could lead to ultrahigh-definition and ultrahigh-precision photoelectric displays, with potential applications in augmented reality (AR) and virtual reality (VR) technologies.
Applications and Future Prospects
The breakthroughs in perovskite LED technology hold significant promise for various applications:
- High-End Displays: The improved brightness, color purity, and stability of perovskite LEDs make them ideal for use in high-end display screens.
- Ultra-High-Brightness Lighting: Perovskite LEDs can be used to create low-cost, ultra-bright lighting solutions for various settings.
- Automotive Lighting: Valeo and Appotronics have announced a strategic partnership to offer next-generation automotive front lighting solutions integrating Appotronics’ ALL-in-ONE full-color laser headlight system, enhancing adaptive lighting functionalities and road safety.
- Wearable Lighting and Display Devices: Fiber light-emitting diodes (Fi-LEDs) based on perovskite quantum wires can be used for wearable lighting and display devices, enabling new possibilities in fiber/textile electronics.
- Solar Cells and Photodetectors: Perovskite materials also have broad application potential in solar cells and photodetectors, contributing to advancements in renewable energy and sensing technologies.
China’s Leading Role
China is at the forefront of perovskite LED research and development, driven by significant investments in R&D, strategic industrial planning, and collaborations between manufacturers and leading research institutions. The Chinese government has designated LED manufacturing as a key sector in its industrial development plans, such as the “Made in China 2025” initiative, further solidifying the country’s position as a global leader in this field.
Top Lighting Companies in China
Several Chinese lighting companies are making significant contributions to the advancement of LED technology:
- Opple Lighting: Known for its high-quality products and commitment to energy efficiency and sustainability.
- Philips Lighting (Signify): A global giant with a strong presence in China, specializing in smart lighting and connected lighting systems.
- NVC Lighting: Recognized for its massive product range and focus on intelligent lighting solutions and green technology.
- Foshan Lighting: One of the pioneers of the lighting industry in China, with a diverse product offering and a focus on energy efficiency.
- TCL Lighting: Leveraging its expertise in IoT and AI to develop innovative smart lighting systems.
These companies, along with numerous research institutions and universities, are driving innovation and shaping the future of the lighting industry in China and beyond.
Challenges and Future Directions
While significant progress has been made in perovskite LED technology, several challenges remain:
- Long-Term Stability: Further research is needed to ensure the long-term stability of perovskite LEDs under various operating conditions.
- Efficiency Optimization: Continued efforts are required to improve the efficiency of perovskite LEDs, particularly at high brightness levels.
- Material Composition: Exploring new material compositions and fabrication techniques to enhance the performance and durability of perovskite LEDs.
- Commercialization: Scaling up production and reducing manufacturing costs to enable the widespread commercialization of perovskite LED technology.
Addressing these challenges will pave the way for perovskite LEDs to become a dominant force in the lighting and display industries, offering energy-efficient, cost-effective, and high-performance solutions for a wide range of applications.
