Synthesis of all-inorganic CsPb2Br5 perovskite and determination of its luminescence mechanism

All-inorganic cesium lead halide perovskite materials, such as CsPbBr3 and CsPb2Br5, have drawn immense attention recently due to their potential applications in optoelectronics. However, unlike the extensively-studied CsPbBr3, many of the fundamental properties of CsPb2Br5 remain unclear, such as its electronic structure and photoluminescence (PL) mechanism. In this work, we developed a novel environmentally friendly chemical method to synthesize CsPb2Br5, where only water and ethanol were used as solvents. The optical property and electronic structure of CsPb2Br5 were then examined both experimentally and theoretically. For the first time we found that the band-edge emission of CsPb2Br5 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 CsPb2Br5 and CsPbBr3, we propose that previously-reported visible emission might be due to the involvement of CsPbBr3 during sample preparation. Overall, this study presents a novel green method for the preparation of CsPb2Br5 and clarifies the optical properties and electronic structure of CsPb2Br5.