Biexciton Emission in CsPbBr<sub>3</sub> Nanocrystals:\nPolar Facet Matters

The\nmetal halide perovskite nanocrystals exhibit a remarkable tolerance\nto midgap defect states, resulting in high photoluminescence quantum\nyields. However, the potential of these nanocrystals for applications\nin display devices is hindered by the suppression of biexcitonic emission\ndue to various Auger recombination processes. By adopting single-particle\nphotoluminescence spectroscopy, herein, we establish that the biexcitonic\nquantum efficiency increases with the increase in the number of facets\non cesium lead bromide perovskite nanocrystals, progressing from cube\nto rhombic dodecahedron to rhombicuboctahedron nanostructures. The\nobserved enhancement is attributed mainly to an increase in their\nsurface polarity as the number of facets increases, which reduces\nthe Coulomb interaction of charge carriers, thereby suppressing Auger\nrecombination. Moreover, Auger recombination rate constants obtained\nfrom the time-gated photon correlation studies exhibited a discernible\ndecrease as the number of facets increased. These findings underscore\nthe significance of facet engineering in fine-tuning biexciton emission\nin metal halide perovskite nanocrystals.