Letter pubs.acs.org/JPCL
Zero-Dimensional Cs4PbBr6 Perovskite Nanocrystals Yuhai Zhang, Makhsud I. Saidaminov,† Ibrahim Dursun, Haoze Yang, Banavoth Murali,‡ Erkki Alarousu, Emre Yengel, Buthainah A. Alshankiti, Osman M. Bakr,* and Omar F. Mohammed* King Abdullah University of Science and Technology, KAUST Solar Center, Division of Physical Sciences and Engineering, Thuwal 23955-6900, Kingdom of Saudi Arabia
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S Supporting Information *
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 Cs4PbBr6, 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.
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higher PLQY is expected in the form of NCs because such trend was consistently observed in other families of perovskite analogous.1 To date, uniform 0-D Cs4PbBr6 NCs of pure phase have not been reported, largely due to the uncontrolled nucleation rate in those conventional methods. A new synthetic method is urgently needed. Herein, we report a reverse microemulsion method to synthesize Cs4PbBr6 NCs with uniform size distribution around 26 nm. Our method overcomes impurity-phase issue by a deliberate selection of reactants with stoichiometric ratio, resulting in the selective generation of 0-D rhombohedral phase of Cs4PbBr6 NCs with 85% reaction yield. The nanocrystal exhibits 65% PLQY in colloidal solution form and, notably, can be dropcasted to yield a highly luminescent thin film of 54% PLQY. Cs4PbBr6 NCs were synthesized through a modified reverse microemulsion method (Figure 1a).9,15 Typically, a dimethylformamide (DMF) solution of PbBr2, hydrogen bromide (HBr), oleic acid (OA), and oleylamine was injected into a n-hexane solution of cesium oleate and OA under vigorous stirring. The immiscible solvent nature of DMF and hexane leads to the formation of a reverse microemulsion system of an “oil” phase with hexane and an “aqueous” phase with DMF. Previous study has demonstrated that the nucleation of 0-D phase Cs4PbBr6 tends to occur at the interface of two solvents with large polarity disparity.9 However, the nucleation rate was not controlled properly, resulting in an irregular morphology of Cs4PbBr6 particles.
ll-inorganic perovskite (CsnPbX2+n) NCs are the current subject of extensive exploration in optoelectronic materials due to their versatile photoluminescence properties, such as high photoluminescence quantum yield (PLQY, >80%) in solution, tunable bandgap, and narrow full width at halfmaximum (fwhm,
