Inter-Conversion between Different Compounds of Ternary Cs-Pb-Br System

The perovskite CsPbBr3attracts great attention due to its potential in optoelectronics. However, stability remains a major obstacle to achieving its effecting application. In this work, we prepared CsPbBr3solids through a simple reaction and investigated reversible conversion between CsPbBr3, Cs4PbBr6, and CsPb2Br5. We found that CsPbBr3can be respectively converted to Cs4PbBr6or CsPb2Br5by reacting with CsBr or PbBr2. Thermodynamic analysis demonstrated that the chemical reactions above were exothermic and occurred spontaneously. Moreover, the formed Cs4PbBr6could be converted to CsPbBr3reversely, and then progressively converted to Cs-deficient CsPb2Br5by extraction of CsBr with water. The CsPb2Br5was converted to CsPbBr3reversely under thermal annealing at 400 °C. The thermodynamic processes of these conversions between the three compounds above were clarified. Our findings regarding the conversions not only provide a new method for controlled synthesis of the ternary Cs-Pb-Br materials but also clarify the underlying mechanism for the instability of perovskites CsPbBr3.