Photoluminescent Nano-CsPbBr<sub>3</sub> Embedded in Cs<sub>4</sub>PbBr<sub>6</sub> Crystals: Formation Mechanism and Properties
Weihao Sun, Yuan‐Ting Hung, Wen‐Tse Huang, Ru‐Shi Liu, Wuzong Zhou
Abstract
High Resolution Image Download MS PowerPoint Slide Luminescent crystalline cesium lead bromide has been synthesized by using an antisolvent method with the nominal ratio of Cs:Pb in the precursors varying in a wide range from 4.5:1 to 1:1. Although the powder X-ray diffraction patterns of all the specimens show Cs 4 PbBr 6 as a pure phase or a main phase, high-resolution transmission electron microscopy images reveal a large amount of CsPbBr 3 nanocrystallites embedded in all the Cs 4 PbBr 6 crystals. A formation mechanism of these perovskite nanocrystallites serving as actual active centers of photoluminescence is proposed. The most crucial step in the crystal growth is the deposition of a noncrystalline coating layer containing polymerized PbBr 6 4– linked by Cs + with the Cs:Pb ratio of about 3:1, and therefore, the actual crystal growth sites are at the interface between the crystal and the coating layer, instead of the crystal/solution interface. The local lack of Cs during the formation of Cs 4 PbBr 6 results in the formation of CsPbBr 3 nanocrystallites inside the parent crystals of Cs 4 PbBr 6 . The photoluminescence quantum yield and stability of the embedded CsPbBr 3 nanocrystallites are significantly improved in comparison with bare CsPbBr 3 crystals. Such simultaneous growth of parent crystals and the embedded nanocrystallites sheds light on further development of cesium lead halide-based photoluminescent materials.