Perovskite quantum dots have great potential as quantum emitters, but their inherent instability has thus far hampered their acceptance. Professor Hao-Wu Lin of the Department of Materials Science and Engineering, Associate Professor Chih-Sung Chuu of the Department of Physics, and Professor Richard Schaller of the Department of Chemistry at Northwestern University in the United States have jointly developed a perovskite quantum emitter with high stability and self-healing ability by a self-developed, simple, and economical procedure—spray-synthesis method. The unprecedented single-photon brightness of these quantum dots is said to break the world-record.

Lin said that in contrast with other quantum emitters, perovskite quantum dots can realize single photon emission at room temperature and have excellent optical properties, such as high quantum yield and high color purity, making them ideal for displays and high-speed computing and communications.

The traditional method of preparing perovskite quantum dots is to directly inject and mix two different solutions. By contrast, Lin's research team has developed a spray-synthesis method which greatly increases the contact area of two different solutions, making it possible to grow a uniform protective organic layer on the surface of the quantum dots. Consequently, the perovskite quantum dots retain their brightness even after 24 hours of intensive continuous excitation, indicating that they could overcome the poor stability of perovskite quantum dots.

The team was surprised to learn that the perovskite quantum dots prepared in this way also have a unique self-healing ability. Although the quantum dots are damaged and decayed by extremely high-intensity excitation, they retrieve their original brightness after "resting" for just a few minutes.

Lin compares researchers to chefs, and correlates preparing quantum dots with making dumplings. Some have tried using different materials, others have tried using thicker wrappers, and still others have tried doubling the wrappers, but he adopted a different approach: He simply kept on refining the method used for wrapping the dumplings.

The first author of the journal paper, NTHU doctoral student Bo-Wei Hsu, recalls the moment when he first witnessed the self-healing capability of quantum dots: "Following a period of strong excitation, the quantum dots gradually dimmed, but after a short while, they recovered their original brightness, and I could hardly believe my eyes!" Hsu did the experiments repeatedly and eventually confirmed that the quantum dots indeed possess this self-healing ability.



Lin pointed out that a perovskite quantum emitter prepared by this spray synthesis method requires only about 1% of the excitation intensity needed for other quantum emitters, and its single-photon brightness is as high as 9 million photons per second, which is a new world record. In addition, its single-photon purity is quite high as 98%.

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