Colloidal quantum‐dot light‐emitting diodes (QDLEDs) with the HfO2/SiO2‐distributed Bragg reflector (DBR) structure are fabricated using a pulsed spray coating method. Pixelated RGB arrays, 2‐in. wafer‐scale white light emission, and an integrated small footprint white light device are demonstrated. The experimental results show that the intensity of red, green, and blue (RGB) emission exhibited considerable enhancement because of the high reflectivity in the UV region by the DBR structure, which subsequently increases the use in the UV optical pumping of RGB QDs. A pulsed spray coating method is crucial in providing uniform RGB layers, and the polydimethylsiloxane (PDMS) film is used as the interface layer between each RGB color to avoid cross‐contamination and self‐assembly of QDs. Furthermore, the chromaticity coordinates of QDLEDs with the DBR structure remain constant under various pumping powers in the large area sample, whereas a larger shift toward high color temperatures is observed in the integrated device. The resulting color gamut of the proposed QDLEDs covers an area 1.2 times larger than that of the NTSC standard, which is favorable for the next generation of high‐quality display technology.
We
synthesized nitrogen (N)-doped graphene quantum dots (N-GQDs)
using a top-down hydrothermal cutting approach. The concentration
of N dopants was readily controlled by adjusting the concentration
of the N source of urea. When N dopants were incorporated into GQDs,
visible absorption was induced by C–N bonds, which created
another pathway for generating photoluminescence (PL). Time-resolved
PL data revealed that the carrier lifetime of GQDs was increased upon
doping with the optimized N concentration. The photoelectrochemical
properties of N-GQDs toward water splitting were studied, and the
results showed that 2N-GQDs prepared with 2 g of urea produced the
highest photocurrent. The photocatalytic activity of 2N-GQDs powder
photocatalyst for hydrogen production was also examined under AM 1.5G
illumination, showing substantial enhancement over that of pristine
GQDs. Electrochemical impedance spectroscopy data further revealed
a significant improvement in charge dynamics and reaction kinetics
and an increased carrier concentration as a result of N doping.
Self‐assembled vertical heterostructure with a high interface‐to‐volume ratio offers tremendous opportunities to realize intriguing properties and advanced modulation of functionalities. Here, a heterostructure composed of two visible‐light photocatalysts, BiFeO3 (BFO) and ε‐Fe2O3 (ε‐FO), is designed to investigate its photoelectrochemical performance. The structural characterization of the BFO‐FO heterostructures confirms the phase separation with BFO nanopillars embedded in the ε‐FO matrix. The investigation of band structure of the heterojunction suggests the assistance of photoexcited carrier separation, leading to an enhanced photoelectrochemical performance. The insights into the charge separation are further revealed by means of ultrafast dynamics and electrochemical impedance spectroscopies. This work shows a delicate design of the self‐assembled vertical heteroepitaxy by taking advantage of the intimate contact between two phases that can lead to a tunable charge interaction, providing a new configuration for the optimization of photoelectrochemical cell.
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