Interrogating Local Order in Quantum-Dot-in-Perovskite Solids

To solve modern challenges in sustainable energy generation and advanced sensing/lighting technologies, significant attention is directed toward semiconducting materials with distinct photonic and optoelectronic properties. Receiving particular attention are colloidal Quantum Dots (QDs), solution-processible, fluorescent nanocrystal analogs of II-VI and III-V semiconductors. Quantum confinement effects in QDs give rise to narrow and size-tunable emission linewidths, and desirable properties may be engineered with a host of core, shell, and surface-bound ligand compositions.^[1] Another compelling class of materials, Metal Halide Perovskites (MHPs), are a strong candidate for next generation solar cells. MHPs exhibit high optical absorption and low exciton recombination and also may be synthesized with cost-efficient solution techniques.^[2]<br/><br/>Modern optoelectronic devices benefit from the integration of specialized constituent materials to realize new functionality. Combining the tunability and precise emission of QDs with the intrinsic charge transport properties of MHP is a compelling avenue for advancing LED and solar cell technologies. Heteroepitaxy-enabled combination of QD and MHP pairs with well-matched lattices, results in a heterostructure now known as a Quantum-Dot-in-Perovskite (QDiP) solids.^[3] Initial investigations since 2015 have revealed promising characteristics and performance of heterostructures comprised of lead chalcogenide quantum dots (PbS/PbSe) integrated within methylammonium-lead-iodide (MAPbI₃) perovskite among other QD-perovskite pairings.^[3,4]<br/><br/>In this talk, we present a detailed analysis of local order in PbS-MAPbI₃ QDiP heterostructures via high energy synchrotron X-ray scattering. Three-dimensional diffuse scattering maps of single QDiP crystals reveal static and dynamic deviations from an ideal lattice-matched structrure by the way of local, nearly static lattice defects associated with the interface between QDs and the MHP. Comparison to diffuse scattering of the pure MHPs^[5,6] shows that the presence of the QDs quench the dynamic, local 2D sheets of tetrahedral MHP within a globally cubic phase. Comparison to simulations isolates the contribution of each individual molecular constituent to the local order.<br/><br/>[1] C. R. Kagan, E. Lifshitz, E. H. Sargent, and D. V. Talapin, “Building devices from colloidal quantum dots,” <i>Science</i>, vol. 353, no. 6302, Aug. 2016, doi: 10.1126/science.aac5523.<br/>[2] X. Qi <i>et al.</i>, “Photonics and Optoelectronics of 2D Metal-Halide Perovskites,” <i>Small</i>, vol. 14, no. 31, p. 1800682, Aug. 2018, doi: 10.1002/smll.201800682.<br/>[3] Z. Ning <i>et al.</i>, “Quantum-dot-in-perovskite solids,” <i>Nature</i>, vol. 523, no. 7560, pp. 324–328, Jul. 2015, doi: 10.1038/nature14563.<br/>[4] H. Chen, J. M. Pina, Y. Hou, and E. H. Sargent, “Synthesis, Applications, and Prospects of Quantum-Dot-in-Perovskite Solids,” <i>Adv. Energy Mater.</i>, p. 2100774, May 2021, doi: 10.1002/aenm.202100774.<br/>[5] N. Weadock, private communication, Oct. 2021<br/>[6] T. Lanigan-Atkins <i>et al.</i>, “Two-dimensional overdamped fluctuations of the soft perovskite lattice in CsPbBr3,” <i>Nature Materials</i>, vol. 20, no. 7, pp. 977–983, Jul. 2021, doi: 10.1038/s41563-021-00947-y.