Author: Zhang Nan
When Xiang Chaoyu decided to make the leap from the industrial sector to scientific research institutions, he already had over 15 years of R&D experience under his belt, holding numerous patents both domestically and internationally. However, despite his extensive experience, he always felt there was a slight distance from the cutting edge of scientific research.
In 2019, Xiang Chaoyu was appointed as a researcher at the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences (hereinafter referred to as "Ningbo Materials Institute"), embarking on a journey to bridge this gap.
"Our past experiences have always been the cornerstone of our work," says Xiang Chaoyu. His team's latest paper was recently published in Nature Photonics, breaking through the "last mile" of perovskite luminescence with a technique called "solvent sieving."
Different perovskite materials and perovskite light-emitting diodes (LEDs) exhibit bright fluorescence under UV light.
Identifying the key factors of instability.
Recently, the advanced nanophotonic materials and devices team led by Chao Yu has developed highly efficient perovskite LEDs, solving the intrinsic stability issues of perovskite materials. Perovskite materials, as one of the most promising photonic materials currently, have outstanding optoelectronic properties and low fabrication costs. Compared to conventional OLED technology, perovskite LEDs can increase color purity by at least twice. However, the poor operational stability has been a major obstacle to practical applications. To address this, the team conducted a detailed analysis of the fine structure of representative quasi-2D perovskite materials and found that the thinner nanosheets with only 1 or 2 layers of lead ions inside were the key source of perovskite instability. Ding Shuo, the first author of the paper and a doctoral student at Ningbo Institute of Materials, explained that the thinner nanosheets are formed by a rapid and uncontrollable crystallization process, resulting in poor crystallization quality and numerous defects, which easily decompose and further induce the overall decomposition of perovskite films, greatly reducing the stability of perovskite materials. Then, the next challenge arose: nanoscale thin sheets tightly packed with other structures, conventional macroscopic processing methods are difficult to accurately remove them. Ding Shuo tried many methods, initially following the ideas of others and adding additives, but too many additives still affected stability. After a series of analyses aimed at simplification, inspired by the sieve that can separate sand grains of different sizes, the research team developed the "solvent sieving" method.
Constantly improving amid skepticism.
"Solvent sieving" is a combination of polar and non-polar solvents. Researchers take advantage of the easy solubility of thinner nanosheets in polar solvents and precisely remove them by adjusting the proportion of polar solvents, without affecting other structures in perovskite materials.
The schematic diagram of the "solvent screening" method (left); the efficiency and lifespan of LEDs prepared using the "solvent screening" method far outperform others (right).
After employing this method to remove thin nanosheets, perovskite materials exhibit remarkable stability, maintaining luminescent performance for over 100 days in humid air. Perovskite LEDs prepared with this material demonstrate a lifespan exceeding 50,000 hours at a brightness of 100 candela per square meter—equivalent to 5.7 years of operation—the highest among all commercial green perovskite LEDs, meeting the requirements for commercial applications. Additionally, the external quantum efficiency of perovskite LEDs reaches 29.5%, a new record for perovskite LED efficiency without light extraction design. While the data is promising, publication wasn't a smooth journey. It took over two years from submission to publication for this achievement. "Initially, reviewers had doubts about these results. Over the two years, we provided numerous explanations and arguments," said Xiang Chaoyu, emphasizing the necessity for confidence, patience, and scientific spirit during this process. "Encountering skepticism from experts is normal. In fact, through this process, the article has made significant progress, and our approach to problem-solving has become more diversified." After 10 rounds of revisions, the evidence became more robust, and the theoretical explanations became more comprehensive. Reviewers ultimately acknowledged the ultra-high efficiency and operational stability of perovskite LEDs in this study, as well as the researchers' identification of the key sources of perovskite instability and their successful precise screening of perovskite structures using the "solvent screening" method.
Furthermore, there's good news as another paper from the same team is about to be published in a prestigious academic journal. The Future Market Is in China
Xiang Chaoyu has previously worked at Apple Inc. and Universal Display Corporation in the United States, participating as a key executor in projects and leading projects funded by the U.S. Department of Energy's Basic Science Program and the U.S. National Science Foundation's Small Business Innovation Research Program. He has also led the development of next-generation OLED and quantum dot LED display technologies. With such an impressive background, Xiang Chaoyu returned to China in 2016 and joined the Industrial Research Institute of TCL, a renowned enterprise. "The reason for returning to China is twofold: my parents and relatives are here, and I also see clearly that the future of the industry lies in China." His team has developed the world's first prototypes of 5-inch full-color AM-QLED and 31-inch full-color AM-HQLED inkjet printers, establishing a series of core device preparation technologies with independent intellectual property rights and obtaining more than 30 domestic and international patents. In September 2019, Xiang Chaoyu joined the Ningbo Institute of Materials, embarking on more cutting-edge scientific research and advancing towards technological high grounds. Being the "Knocking" Pivot
Having worked at the Ningbo Institute of Materials for four and a half years, Xiang Chaoyu feels a greater sense of responsibility. Whether it's scientific research layout, talent structure, student cultivation, or project acquisition, nothing can be taken lightly.
Xiang Chao Yu (left) and Ding Shuo, both teachers and students, are conducting experimental operations.
"These past few years have been about learning how to be better researchers. The next four years will be about 'making blood' ourselves," Xiang Chao Yu said. Speaking about the results published this time, he believes that the widespread attention to perovskite materials in research has only been around for less than 10 years, making it a new "IP" with many potential areas for development. "Many advanced semiconductor manufacturing materials are controlled by others." Xiang Chao Yu sees the development of this material as reaching a turning point. With years of experience in quantum dot LED research and strong support from the institute, he believes his team has the capability to become the pioneers in tackling this turning point, fundamentally addressing some critical issues. "Of course, we have only overcome the lifespan and efficiency issues of perovskite light-emitting diodes in green light. Challenges with blue light, red light, and others still need to be addressed. The next step is to see if we can improve by several orders of magnitude and move closer to industrial applications," Xiang Chao Yu said. "Solving practical problems has always been our driving force. Staying true to our original intentions in our work keeps us on track."
Related paper information: https://doi.org/10.1038/s41566-023-01372-0
