Organic–inorganic hybrid lead halide perovskite nanocrystals (PeNCs) have received great attention as a light source for perovskite LEDs (PeLEDs) owing to the superior optical properties. However, PeNCs typically use octylamine (OAm) as capping ligands which have insulating properties. Exploring a desirable short alkylamine instead of OAm is required for the improvement of PeLEDs. Here, as one of the strategies to solve this issue, the effects of alkylamine chain length for optical properties of PeNCs and PeLED characteristics are investigated. Pentylamine is an optimal short alkylamine and precipitate luminescent PeNCs with high PLQY values of 90%. Importantly, pentylamine maintains a relatively high PLQY of 48% after spin-coating, due to the durability pentylamine has to ethyl acetate as a washing solvent. PeNCs capped with pentylamine also demonstrate an external quantum efficiency of over 1% with luminance of over 2000 cd cm−2, indicating that pentylamine has the potential to overcome the insulator properties of PeNC thin film.
Owing
to their excellent photoluminescence (PL) properties in a
narrow linewidth below 30 nm and high photoluminescence quantum yield
(PLQY), organometal halide perovskite nanocrystals (PeNCs) are promising
photonic sources for wide-color gamut displays. However, with a top-down
approach, luminescent PeNCs comparable to those prepared through bottom-up
synthesis is still a significant subject, including the optimization
of milling processes. Herein, we propose a novel and simple ultrasound-assisted
bead milling process based on the characteristics of facile crystallization.
During the milling process, irradiated ultrasounds disperse milling
beads that facilitate an intense collision between the beads and the
perovskite precursors. Thus, this bead milling can be easily performed
without planetary ball milling, and it provides brightly luminescent
colloidal PeNCs with high PLQY. We established that mechanochemical
conditions significantly enhance the optical properties by exploring
various milling conditions. Furthermore, the color adjustment can
be realized by changing the halide composition. Therefore, this novel
milling process has great potential and versatility for preparing
diverse perovskite nanomaterials for optoelectronic applications.
Synthesized MAPbI3 QDs were purified using various alkyl acetates, with differences in the dispersibility of the MAPbI3 QDs in each solvent, and an LED based on the purified MAPbI3 QDs showed narrow emission and a high external quantum efficiency.
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%.
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