Biexciton Auger Recombination in Strongly Confined Perovskite Quantum Dots and its Correlation to Photoluminescence Blinking

Lead halide perovskite quantum dots (QDs) are promising single photon emitters owing to their high room temperature luminescence efficiency and solution processibility. Moreover, strongly confined perovskite QDs (SCPQDs), whose physical sizes are much smaller than their Bohr diameters, are predicted to have high single photon emission purity due to their ultra-fast biexciton Auger recombination rates. Recent advances have demonstrated that reducing the sizes of perovskite QDs leads to higher single photon emission purities. It is also known that biexciton emission quantum yield can be estimated by the g^₂(0) values from the second-order photon correlation measurements. However, studies on single perovskite QDs have witnessed unexpectedly low single photon emission purities with g²(0) values varying dramatically. Additionally, perovskite QDs often show severe fluorescence intensity fluctuations. Recently, we have developed a QD-in-matrix method that can successfully passivate and disperse SCPQDs with improved photostability. By controlling the surface passivation conditions, we have studied over 1000 single SCPQDs and correlated their fluorescence blinking behaviors with their g²(0) values. We found that perovskite QDs with high "ON" time fraction show significantly lower biexciton emission efficiency. The biexciton emissions from perovskite QDs with high "OFF" fraction are more efficient. Such a positive correlation between QD "OFF" time fractions and biexciton emission quantum yields is opposite to what has been revealed in CdSe core-shell QDs, and it suggests that the Auger recombination rate can change with respect to the surface conditions of the perovskite QDs. We propose a model that combines both exciton trapping and exciton-surface lattice interaction for different biexciton emission quantum yields observed in SCPQDs.