Crown ether-assisted room-temperature halide passivation for high-efficiency PbS quantum dots enabling large-area and long-lifetime near-infrared QD-OLEDs

High-efficiency and low-cost near-infrared (NIR) emitting quantum dots (QDs) are highly desirable for next-generation intrinsically flexible NIR light sources. Halide passivation is commonly employed to passivate surface traps to obtain high-quality NIR-emitting PbS QDs, but this procedure requires high temperature and inert atmospheres. Here we develop a facile room-temperature halide passivation method for highly efficient NIR-emitting PbS QDs by employing crown ethers as a unique auxiliary additive. Experimental and theoretical investigations reveal that the formation of K+-crown ethers complex effectively facilitates the dissociation of KCl in toluene and releases more Cl- ions for extraordinary halide passivation at room temperature and in the air, thus improving the photoluminescence quantum yield from 24% to 35% in solution and further to 44% in blend films. The well-passivated PbS QD films are integrated with red organic light-emitting diodes (OLEDs) and the resulting QD-OLEDs exhibit high-performance NIR emission centered at 887 nm, a high external quantum efficiency of 5.2% at a radiance of 10 W.sr(-1).m(-2), and superior operational stability with long lifetime T-90 of 188 h at the current density of 25 mA.cm(-2). We also construct a large-area NIR QD-OLED (5 cm x 5 cm) with desirable uniform emission. This work opens a new avenue to achieve robust large-area NIR planar light sources for broad applications.