Water-Assisted Perovskite Quantum Dots with High Optical Properties

Lead halide perovskite quantum dots (PeQDs) have excellent optical properties, such as narrow emission spectra (FWHM: 18–30 nm), a tunable bandgap (λPL: 420–780 nm), and excellent photoluminescence quantum yields (PLQYs: >90%). PeQDs are known as a material that is easily decomposed when exposed to water in the atmosphere, resulting in causing PeQDs to lower performance. On the other hand, according to the recent reports, adding water after preparing the PeQD dispersion decomposed the PeQD surface defects, resulting in improving their PLQY. Namely, controlling the amount of assisting water during the preparation of the PeQDs is a significantly critical factor to determining their optical properties and device applications. In this paper, our research group discovered the novel effects of the small amount of water to their optical properties when preparing the PeQDs. According to the TEM Images, the PeQDs particle size was clearly increased after water-assisting. In addition, XPS measurement showed that the ratio of Br/Pb achieved to be close to three. Namely, by passivating the surface defect using Ostwald ripening, the prepared PeQDs achieved a high PLQY of over 95%.