Selective synthesis of pure CsPbBr3 and pure Cs4PbBr6 nanocrystals towards the fine control of their emission properties

Perovskite nanocrystals (NCs) have garnered significant attention owing to their remarkable optoelectronic properties, making them promising candidates for various applications such as light-emitting diodes, photodetectors, and solar cells. Among perovskite NCs, cesium lead halide (CsPbX ₃ ) and tetracesium lead hexahalide (Cs ₄ PbX ₆ ) are of particular interest due to their tunable bandgap and excellent photoluminescence characteristics. Herein, we present a comparative study on the selective synthesis of CsPbBr ₃ and Cs ₄ PbBr ₆ NCs, elucidating the distinct reaction pathways, controlling parameters governing their formation and unveil the non-luminescent properties of pure Cs ₄ PbBr ₆ nanocrystals. We employ a facile hot-injection method utilizing benzoyl bromide as a unique bromide source, to synthesize both CsPbBr ₃ and Cs ₄ PbBr ₆ NCs. Through systematic variation of precursor ratios and reaction temperature, we achieve precise control over nanocrystal morphology, crystallinity and phase purity. A detailed structural characterization reveals the formation of well-defined CsPbBr ₃ and Cs ₄ PbBr ₆ NCs and highlights the importance of combining complementary techniques to unambiguously identify the crystalline phase. Optical investigations show that phase-pure Cs ₄ PbBr ₆ NCs synthesized at low injection temperatures are intrinsically non-emissive, whereas samples obtained at higher injection temperatures exhibit weak emission with spectral features resembling those of CsPbBr ₃ NCs, particularly after thermal annealing. Thermal annealing of NC thin films enhances their adhesion to the substrate, enabling potential multilayer fabrication and inducing slight shifts in the emission spectra. Notably, we extended our synthesis methodology to the selective synthesis of cesium lead chloride (CsPbCl ₃ ) and tetracesium lead hexachloride (Cs ₄ PbCl ₆ ) NCs using benzoyl chloride, demonstrating the versatility and reproducibility of the synthetic pathway.