Mechanistic Investigation of the Defect Activity Contributing to the Photoluminescence Blinking of CsPbBr₃ Perovskite Nanocrystals

Abstract

Exploration of the full potential of the perovskite nanocrystals (NCs) for different applications requires a thorough understanding of the pathways of recombination of the photogenerated charge carriers and associated dynamics. In this work, we have tracked the recombination routes of the charge carriers by probing photoluminescence (PL) intermittency of the immobilized and freely diffusing single CsPbBr3 NCs employing a time-tagged-time-resolved method. The immobilized single CsPbBr3 NCs show a complex PL time-trace, a careful analysis of which reveals that nonradiative band-edge recombination through trap states, trion recombination, and trapping of the hot carriers contribute to the blinking behavior of any given NC. A drastically suppressed PL blinking observed for the NCs treated with a tetrafluoroborate salt indicates elimination of most of the undesired recombination processes. A fluorescence correlation spectroscopy (FCS) study on the freely diffusing single NCs shows that enhanced PL and suppressed blinking of the treated particles are the outcome of an increase in per-particle brightness, not due to any increase in the number of particles undergoing “off”–“on” transition in the observation volume. The mechanistic details obtained from this study on the origin of blinking in CsPbBr3 NCs provide deep insight into the radiative and nonradiative charge carrier recombination pathways in these important materials, and this knowledge is expected to be useful for better design and development of bright photoluminescent samples of this class for optoelectronic applications.

Synthesis and Localized Photoluminescence Blinking of Lead‐Free 2D Nanostructures of Cs3Bi2I6Cl3 Perovskite

“…Notably, time trace of individual NC shows that rather than a completely non‐emissive or dark state, the NC exhibit a “dim” off state. The blinking pattern of this nature is previously reported for CsPbBr 3 NCs . The emission intensities corresponding to the many of these “dim” off states are slightly above the background intensity level.…”

Presence of Maximal Characteristic Time in Photoluminescence Blinking of MAPbI3 Perovskite

“…The first one is the Auger mechanism introduced by Efros and Rosen. [59] This mechanism which is also called charging mechanism, [60] A-type blinking mechanism, [61] Augerblinking, [62] AC blinking, [63] and Type I blinking [64] is based on fast Auger recombination of the photoexcited state of the ionized nanocrystal. Thus, in the Auger mechanism, blinking is a result of ionization-neutralization cycles.…”

Guidelines for the characterization of metal halide nanocrystals

“…The study of the physical properties of MH NCs is a vivid field of research relying on various continuous-wave and time-resolved optical spectroscopies performed under controlled temperature [55][56][57][58][59][60] and environmental conditions [61][62][63] at both the ensemble and the single-particle level (Figure 4) [64][65][66][67]. This enables us to build a comprehensive photophysical picture including the bandgap energy [20,27], the emission spectrum and its excitonic versus defect/dopantbased contributions [6,[68][69][70][71][72], the exciton [73] and biexciton binding energies [74], and the rates of radiative and nonradiative processes in single NC and ensembles [75][76][77] and in hybrid architectures [78][79][80][81][82], as well as the extent of blinking processes and single-photon emission properties [64][65][66][67] (Figure 4). Overall, this information offers design guidelines for the engineering of perovskite NCs with optical properties tailored for specific applications.…”