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

The perovskite CsPbBr(3) attracts great attention due to its potential in optoelectronics. However, stability remains a major obstacle to achieving its effecting application. In this work, we prepared CsPbBr(3) solids through a simple reaction and investigated reversible conversion between CsPbBr(3), Cs(4)PbBr(6), and CsPb(2)Br(5). We found that CsPbBr(3) can be respectively converted to Cs(4)PbBr(6) or CsPb(2)Br(5) by reacting with CsBr or PbBr(2). Thermodynamic analysis demonstrated that the chemical reactions above were exothermic and occurred spontaneously. Moreover, the formed Cs(4)PbBr(6) could be converted to CsPbBr(3) reversely, and then progressively converted to Cs-deficient CsPb(2)Br(5) by extraction of CsBr with water. The CsPb(2)Br(5) was converted to CsPbBr(3) reversely 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 CsPbBr(3).