Photophysical properties of wavelength-tunable methylammonium lead halide perovskite nanocrystals

Abstract

We present the time-correlated luminescence of isolated nanocrystals of five methylammonium lead mixed-halide perovskite compositions (CH₃NH₃PbBr_3−xI_x) that were synthesized with varying iodide and bromide anion loading. All analyzed nanocrystals had a spherical morphology with diameters in the range of 2 to 32 nm. The luminescence maxima of CH₃NH₃PbBr_3−xI_x nanocrystals were tuned to wavelengths ranging between 498 and 740 nm by varying the halide loading. Both CH₃NH₃PbI₃ and CH₃NH₃PbBr₃ nanocrystals exhibited no luminescence intermittency for more than 90% of the 250 s analysis time, as defined by a luminescence intensity three standard deviations above the background. The mixed halide CH₃NH₃PbBr_0.75I_0.25, CH₃NH₃PbBr_0.50I_0.50, and CH₃NH₃PbBr_0.25I_0.75 nanocrystals exhibited luminescence intermittency in 18%, 4% and 26% of the nanocrystals, respectively. Irrespective of luminescence intermittency, luminescence intensities were classified for each nanocrystal as: (a) constant, (b) multimodal, (c) photobrightening, and (d) photobleaching. Based on their photophysics, the CH₃NH₃PbBr_3−xI_x nanocrystals can be expected to be useful in a wide-range of applications where low and non-intermittent luminescence is desirable, for example as imaging probes and in films for energy conversion devices.