Cell refinement of CsPbBr 3 perovskite nanoparticles and thin films.

In this work, we performed a detailed study of the phase transformations and structural unit cell parameters of CsPbBr 3 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 CsPbBr 3 thin films upon annealing and transmission electron microscopy gives physical and crystallographic information for the CsPbBr 3 NPs using electron diffraction. The secondary phase(s) CsPb 2 Br 5 (and CsPb 4 Br 6 ) 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 CsPb 2 Br 5 secondary phase disappears completely above 580 K and pure cubic CsPbBr 3 is observed up to 623 K. The CsPbBr 3 phase is then kept upon cooling down to RT, achieving pure CsPbBr 3 phase. This study provides detailed understanding of the phase behavior vs. temperature of CsPbBr 3 NPs and thin films, which opens the way to pure CsPbBr 3 phase, an interesting material for optoelectronic applications.