Infrared lead chalcogenide quantum dots (QDs) suffer fast degradation due to the easy oxidation of surface chalcogen atoms. Here, we report a trioctylphosphine-mediated surface passivation method to improve the air stability of PbS QDs. Surface mechanism study reveals an in situ surface reaction, which leads to site-selective passivation of surface S atoms with lead mono-carboxylate. The surface capping motif sufficiently protects PbS QDs from oxygen and improves their stability as well as quantum efficiency regardless of the QD size and original ligands on surface cations. The modified PbS QDs display no obvious fluorescence quenching and surface oxidization after 30 days of air exposure. The robust surface capping also provides high compatibility of PbS QDs with polymers for optoelectronic device fabrication. The near-infrared LEDs based on the modified PbS QDs display a slight degradation of only 1.47% from the maximum intensity after continuous operation in air for 250 hours (lifetime > 10,000 h) at 0.5 W/cm² power density, indicating the surface passivation route is promising strategy for promoting practical optoelectronic application of PbS QDs.

The hole injection is one of the bottlenecks that strongly hinder the quantum efficiency and the optical power for deep ultraviolet light-emitting diodes (DUV LEDs) with the emission wavelength smaller than 360 nm. The hole injection efficiency for DUV LEDs is co-affected by the p-type ohmic contact, the p-type hole injection layer, the p-type electron blocking layer and the multiple quantum wells. In this report, we review a large diversity of advances that are currently adopted to increase the hole injection efficiency for DUV LEDs. Moreover, by disclosing the underlying device physics, the design strategies that we can follow have also been suggested to improve the hole injection for DUV LEDs.