Amplified Spontaneous Emission in Facet Engineered Metal Halide Perovskite Nanocrystals

Lead halide perovskite nanocrystals exhibiting rich chemical, structural, and optical tunability are at the forefront of current research due to their defect-tolerant electronic structure, extremely narrow absorption and emission line widths, and ability to control their surface or facet chemistry. Significant advances have been achieved in improving device efficiencies by varying ligand, precursor, size of the NCs, and cation-anion compositions, etc. However, all these studies are confined to a six-faceted hexahedron (cube/platelet) shape. In contrast, for the first time, we studied a new design strategy of facet engineering to reduce the gain threshold of amplified spontaneous emission by many-folds in NCs of the same concentration and edge length. We achieved this hallmark result by controlling the Auger recombination rates dominated by processes involving NC volume and thermalization time to the emitting states by optimizing the number of facets from 6 (cube) to 12 (rhombic dodecahedron) and 26 (rhombicuboctahedrons) in CsPbBr3 NCs. For instance, we demonstrate a two-fold reduction in Auger recombination rates and thermalization time with increased number of facets. The gain threshold can be further reduced ∼ 50% by decreasing sample temperature to 4K. Our systematic studies offer a new method to reduce the gain threshold that ultimately forms the basis of nanolasers.