Zero-Dimensional Cs₄PbBr₆ Perovskite Nanocrystals

Abstract

Perovskite nanocrystals (NCs) have become leading candidates for solution-processed optoelectronics applications. While substantial work has been published on 3-D perovskite phases, the NC form of the zero-dimensional (0-D) phase of this promising class of materials remains elusive. Here we report the synthesis of a new class of colloidal semiconductor NCs based on CsPbBr, the 0-D perovskite, enabled through the design of a novel low-temperature reverse microemulsion method with 85% reaction yield. These 0-D perovskite NCs exhibit high photoluminescence quantum yield (PLQY) in the colloidal form (PLQY: 65%), and, more importantly, in the form of thin film (PLQY: 54%). Notably, the latter is among the highest values reported so far for perovskite NCs in the solid form. Our work brings the 0-D phase of perovskite into the realm of colloidal NCs with appealingly high PLQY in the film form, which paves the way for their practical application in real devices.

Zero-Dimensional Cesium Lead Halides: History, Properties, and Challenges

“…11,12 Soon after, the first publications on Cs 4 PbX 6 nanocrystals (NCs) emerged. 13,14 Interestingly, in stark contrast to the highly emissive CsPbX 3 NCs that were first synthesized in 2015 15 and the highly green emitting Cs 4 PbBr 6 powders, some of these Cs 4 PbX 6 NCs exhibited no PL; instead, they had optical properties that were similar to those described in the first reports on Cs 4 PbX 6 in 1893 and in the 1990s. 13 Furthermore, these optical properties were also similar to those of individual [PbBr 6 ] 4– clusters.…”

“…For instance, no CsPbBr 3 diffractions peaks were reported in various Cs 4 PbBr 6 samples, including powders, single crystals, and NCs. 11,14,17,18,20,21 For instance, De Bastiani et al were able to demonstrate that the presence of any CsPbBr 3 impurity phase down to 0.5% in weight could be detected by XRD (Figure 4a). 21 Nevertheless a similar experiment, in which nonluminescent Cs 4 PbBr 6 NCs were mixed with a small amount (2% molar, 0.5 wt %) of highly luminescent CsPbBr 3 NCs, indicated that this small amount of CsPbBr 3 did not result in any clear CsPbBr 3 features in the XRD pattern (Figure 4b).…”

“…13 Furthermore, these optical properties were also similar to those of individual [PbBr 6 ] 4– clusters. 16 The proposed origin of the green PL is either intrinsic to Cs 4 PbBr 6 (due to the presence of defects) 11,12,14,17−26 or from contamination by CsPbBr 3 NC-like impurities. 13,27−42 …”

“…(c) Defect-related PL emission in a layered 2D organic lead bromide ( N 1-methylethane-1,2-diammonium)PbBr 4 , adapted from ref (98). (d) Absorption, PL, and PLE from green-emitting 26 nm Cs 4 PbBr 6 NCs, showing a narrow PL fwhm and strong quenching of the PL at around 315 nm, adapted from ref (14). (e) Absorption and PL of a green-emitting Cs 4 PbBr 6 single crystal, showing narrow band-edge-like PL, adapted from ref (21).…”

“…For instance, unlike CsPbBr 3 and its hybrid perovskite counterpart, which are usually found to be bromine-deficient, 80−83 Cs 4 PbBr 6 is often reported to have a Br:Pb ratio that is usually higher than 6, thus implying that Cs 4 PbBr 6 are rather halide rich. 14,18,20,80 One could therefore expect a rather low density of V Br .…”