All-inorganic cesium lead halide perovskite materials, such as CsPbBr 3 and CsPb 2 Br 5 , have drawn immense attention recently due to their potential applications in optoelectronics. However, unlike the extensivelystudied CsPbBr 3 , many of the fundamental properties of CsPb 2 Br 5 remain unclear, such as its electronic structure and photoluminescence (PL) mechanism. In this work, we developed a novel environmentally friendly chemical method to synthesize CsPb 2 Br 5 , where only water and ethanol were used as solvents.The optical property and electronic structure of CsPb 2 Br 5 were then examined both experimentally and theoretically. For the first time we found that the band-edge emission of CsPb 2 Br 5 was not in the visible range as reported in the literature but rather located in the ultraviolet range. By monitoring the PL property during phase conversion between CsPb 2 Br 5 and CsPbBr 3 , we propose that previously-reported visible emission might be due to the involvement of CsPbBr 3 during sample preparation. Overall, this study presents a novel green method for the preparation of CsPb 2 Br 5 and clarifies the optical properties and electronic structure of CsPb 2 Br 5 .

The perovskite CsPbBr3 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 CsPbBr3 solids through a simple reaction and investigated reversible conversion between CsPbBr3, Cs4PbBr6, and CsPb2Br5. We found that CsPbBr3 can be respectively converted to Cs4PbBr6 or CsPb2Br5 by reacting with CsBr or PbBr2. Thermodynamic analysis demonstrated that the chemical reactions above were exothermic and occurred spontaneously. Moreover, the formed Cs4PbBr6 could be converted to CsPbBr3 reversely, and then progressively converted to Cs-deficient CsPb2Br5 by extraction of CsBr with water. The CsPb2Br5 was converted to CsPbBr3 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 CsPbBr3.

The exotic physicochemical properties of TM atoms (3d, 4d, and 5d) embedded g-C4N3 as a novel class of 2D monolayers were systematically investigated through hierarchical high-throughput screening combined with spin-polarized...

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