CsPbBr3@Cs4PbBr6 Emitter-in-Host Composite: Fluorescence Origin and Interphase Energy Transfer

Although the superior halide perovskite (HP) nanocrystals (NCs) have garnered considerable research passion in recent years, their practical use is still dauntingly plagued by the instability issue. The so-called "zero-dimensional" (0D) cesium lead HP, equipped with similar fluorescent attributes as those of HP NCs but greatly enhanced stability, has emerged as a promising alternative. Nevertheless, a long-lasting debate over the microstructure and emissive mechanism was ignited then. The research community has been demarcated into two sides holding vastly different opinions, which are known as the earlier Br vacancy scenario and the later CsPbBr3 impurity scenario. The inadequate understanding hinders further fundamental investigations as well as potential applications of the 0D HP. Lately, some highly persuasive experimental evidence, the lack of which was the main cause of the earlier turn to Br vacancy theory, for the CsPbBr3 impurity theory was demonstrated. This Review tries to, with these reports, reproduce a CsPbBr3@Cs4PbBr6 model of 0D HP and present how the CsPbBr3 impurity theory reasonably outcompetes the Br vacancy counterpart regarding shared experimental phenomena. Importantly, energy transfer within the diphase 0D HP, which has been overlooked but determines the optoelectronic/optical performance, is comprehensively discussed. Finally, potential fluorescent applications of 0D HP and corresponding challenges are prospected.