Synthesis of Two-Dimensional CsPb2X5 (X = Br and I) with a Stable Structure and Tunable Bandgap by CsPbX3 Phase Separation

Perovskite-related materials with various dimensionalities have attracted sustained attention owing to their extraordinary electronic and optoelectronic properties, but it is still challenging in the synthesis of compounds with desired compositions and structures. Herein, a two-dimensional (2D) CsPb2I5perovskite has been synthesized by the conversion ofCsPbI3at high-pressure and high-temperature (highP-T) conditions, which is quenchable at ambient conditions .In situ synchrotron X-ray diffraction shows that high-pressure monoclinicCsPbI3converts into tetragonal CsPb2I5and cubic CsI at 8.7 GPa upon heating from 644 to666 K. Keeping the tetragonal structure stable, CsPb2I5exhibits tunable optical properties with the bandgap changing from similar to 2.4 eV at ambient pressure to similar to 1.4 eV at 36.9 GPa. Further experiments demonstrate similar structural evolution in the typical three-dimensional CsPbBr3perovskite into 2D CsPb2Br5at high P-Tconditions, indicating that the conversion of CsPbX3(X = Br and I) into CsPb2X5is ubiquitous.

Automated summary

Perovskite-related materials have attracted sustained attention due to their extraordinary electronic and optoelectronic properties. However, the synthesis of compounds with desired compositions and structures remains challenging. In this study, a two-dimensional CsPb2I5 perovskite was successfully synthesized by converting CsPbI3 under high-pressure and high-temperature conditions. The conversion of CsPbX3 (X = Br and I) into CsPb2X5 was found to be ubiquitous, indicating a similar structural evolution in various perovskite materials.