Surface Regulation of CsPbBr3 Quantum Dots for Standard Blue-Emission with Boosted PLQY

It is demonstrated that, via surface treatment of CsPbBr3 perovskite quantum dots (PeQDs) by introducing small amount of organic ammonium chlorides possessing short alkyl chain (C <= 4) in methyl acetate in the typical purification process, the emission can be tuned from green to blue region with boosted photoluminescence quantum yield (PLQY). The Cl- mainly works on the surface of PeQDs to fill bromide vacancy, which generates a passivated mixed-halide surface and avoids formation of defects deep within bandgap. Meanwhile, the replacement of initial long-chain ligands with short chain ammonium moiety benefits the film PLQY. Accordingly, a standard blue emission of 461 nm with a high film PLQY of 52% is accessed and the corresponding colloidal shows a PLQY of 80% at 456 nm. This method is also proved to be a versatile tool to boost the PLQY of PeQDs by using short chain ammonium halides bearing the same X with the initial CsPbX3. A near-unity colloidal PLQY of 97% and 98% is achieved for CsPbBr3 and CsPbI3 respectively. Quantum dots light-emitting diode (QLED) with treated CsPbBr3 affords a standard blue electroluminescence of 459 nm and a maximum external quantum efficiency of 0.3%.