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

It is demonstrated that, via surface treatment of CsPbBr 3 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 CsPbX 3 . A near‐unity colloidal PLQY of 97% and 98% is achieved for CsPbBr 3 and CsPbI 3 respectively. Quantum dots light‐emitting diode (QLED) with treated CsPbBr 3 affords a standard blue electroluminescence of 459 nm and a maximum external quantum efficiency of 0.3%.