The development of synthetic routes to access stable, ultra-small (i.e. <5 nm) lead halide perovskite (LHP) quantum dots (QDs) is of fundamental and technological interest. The considerable challenges include the high solubility of the ionic LHPs in polar solvents and aggregation to form larger particles. Here, we demonstrate a simple and effective host-guest strategy for preparing ultra-small lead bromide perovskite QDs through the use of nano-sized MOFs that function as nucleating and host sites. Cr3O(OH)(H2O)2(terephthalate)3 (Cr-MIL-101), made of large mesopore-sized pseudo-spherical cages, allows fast and efficient diffusion of perovskite precursors within its pores, and promotes the formation of stable, ∼3 nm-wide lead bromide perovskite QDs. CsPbBr3, MAPbBr3 (MA+ = methylammonium), and (FA)PbBr3 (FA+ = formamidinium) QDs exhibit significantly blue-shifted emission maxima at 440 nm, 446 nm, and 450 nm, respectively, as expected for strongly confined perovskite QDs. Optical characterization and composite modelling confirm that the APbBr3 (A = Cs, MA, FA) QDs owe their stability within the MIL-101 nanocrystals to both short- and long-range interfacial interactions with the MOF pore walls. This journal is
Bibliographical noteFunding Information:
This work was supported by the Army Research Office (grant number W911NF-17-1-0174). We thank Dr R. Day for SEM and Dr J. Gardener for assistance with STEM EDX mapping. L. P. acknowledges the Swiss NSF Postdoctoral Fellowship for support (Grant P2EXP2-172214). J. C. acknowledges the Gen-eralitat Valenciana for the Postdoctoral APOSTD/2017/081 Fellowship. K. W. and W. A. T. were supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under award no. DE-SC0019345. This research was also supported by the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT (2018M3D1A1058536). Computational work used the ARCHER UK National Supercomputing Service (http://www.archer.ac.uk) via the HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202). We thank Mr G. Skorupskii for generating graphics for Fig. 1.
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