Synthesis and luminescence of ultrasmall CsPbBr 3 nanocrystals and CsPbBr 3 /Cs 4 PbBr 6 composites by one‐pot method

All‐inorganic perovskites CsPbX 3 (X = Cl, Br, I) have attracted worldwide interest due to their excellent luminescent performances. Meanwhile, Cs 4 PbBr 6 have been studied because they can enhance the luminescent efficiency and stability of CsPbBr 3 . Herein, we introduced a microfluidic method based on room‐temperature supersaturated recrystallization to synthesize blue‐emitting CsPbBr 3 nanocrystals (NCs) and green‐emitting CsPbBr 3 /Cs 4 PbBr 6 NCs. The ultrasmall CsPbBr 3 NCs emitted at a deep blue wavelength of 461 nm with the full width at half maximum (FWHM) of 15 nm. transmission electron microscopy (TEM) results demonstrated that ultrasmall CsPbBr 3 NCs with the average particle size of 3.8 nm were synthesized and the CsPbBr 3 NCs were crystallized as monoclinic structure. X‐ray photoelectron spectrometer (XPS) analysis suggested that ultrasmall CsPbBr 3 suffered from V Br defect and the surface passivation of Cs 4 PbBr 6 possessed a low level of V Br defect density. The lifetime of CsPbBr 3 /Cs 4 PbBr 6 was much longer than that of CsPbBr 3 . The results showed that ultrasmall CsPbBr 3 NCs can be regarded as a source of blue‐emitting material and CsPbBr 3 /Cs 4 PbBr 6 NCs had a better stability.