Perovskite quantum dots (QDs) are of interest for solution-processed lasers; however, their short Auger lifetime has limited lasing operation principally to the femtosecond temporal regime the photoexcitation levels to achieve optical gain threshold are up to two orders of magnitude higher in the nanosecond regime than in the femtosecond. Here the authors report QD superlattices in which the gain medium facilitates excitonic delocalization to decrease Auger recombination and in which the macroscopic dimensions of the structures provide the optical feedback required for lasing. The authors develope a self-assembly strategy that relies on sodiumd-an assembly director that passivates the surface of the QDs and induces self-assembly to form ordered three-dimensional cubic structures. A density functional theory model that accounts for the attraction forces between QDs allows to explain self-assembly and superlattice formation. Compared to conventional organic-ligand-passivated QDs, sodium enables higher attractive forces, ultimately leading to the formation of micron-length scale structures and the optical faceting required for feedback. Simultaneously, the decreased inter-dot distance enabled by the new ligand enhances exciton delocalization among QDs, as demonstrated by the dynamically red-shifted photoluminescence. These structures function as the lasing cavity and the gain medium, enabling nanosecond-sustained lasing with a threshold of 25 µJ cm-2 .
KAUST Repository Item: Exported on 2021-08-30
Acknowledgements: C.Z., J.M.P., and T.Z. contributed equally to this work. L.Z. and H.D. acknowledge the National Natural Science Foundation of China (Grant Nos. 61875256, 61675219, and 91950201). This work was partially funded by the Natural Sciences and Engineering Research Council of Canada (NSERC). M.I.S. acknowledges the support of Banting Postdoctoral Fellowship Program, administered by the Government of Canada. WAXS and SAXS measurements were performed in the Canadian Light Source CLS, a national research facility of the University of Saskatchewan, which is supported by the Canada Foundation for Innovation (CFI), NSERC, the National Research Council (NRC), the Canadian Institutes of Health Research (CIHR), the Government of Saskatchewan, and the University of Saskatchewan. The authors acknowledge the technical assistance and scientific guidance of C.-Y. Kim and A. Leontowich at the CLS. The authors also acknowledge the help and useful discussions of A. Johnston, S. Teale, and J. Fan regarding the WAXS and SAXS data. They also acknowledge the useful discussions with R. Sabatini regarding transient PL data. H.D. acknowledges the Youth Top-notch Talent Support Program in Shanghai. The authors again acknowledge the University of Chinese Academy of Sciences (UCAS) Joint Ph.D. Training Program.