Cell refinement of CsPbBr₃ perovskite nanoparticles and thin films

In this work, we performed a detailed study of the phase transformations and structural unit cell parameters of CsPbBr₃ nanoparticles (NPs) and thin films. In situ X-ray diffraction patterns were acquired as a function of temperature, where the positions and widths of the diffraction peaks were systematically tracked upon heating and cooling down to room temperature (RT). Scanning electron microscopy provides physical insight on the CsPbBr₃ thin films upon annealing and transmission electron microscopy gives physical and crystallographic information for the CsPbBr₃ NPs using electron diffraction. The secondary phase(s) CsPb₂Br₅ (and CsPb₄Br₆) are clearly observed in the XRD patterns of both nanoparticles and thin films upon heating to 500 K, whilst from 500 K to 595 K, these phases remain in small amounts and are kept like this upon cooling down to RT. However, in the case of thin films, the CsPb₂Br₅ secondary phase disappears completely above 580 K and pure cubic CsPbBr₃ is observed up to 623 K. The CsPbBr₃ phase is then kept upon cooling down to RT, achieving pure CsPbBr₃ phase. This study provides detailed understanding of the phase behavior vs. temperature of CsPbBr₃ NPs and thin films, which opens the way to pure CsPbBr₃ phase, an interesting material for optoelectronic applications.