Emissive Surface Traps Lead to Asymmetric Photoluminescence Line Shape in Spheroidal CsPbBr3 Quantum Dots

Abstract

The morphology of quantum dots plays an important role in governing their photophysics. Here, we explore the photoluminescence of spheroidal CsPbBr₃ quantum dots synthesized via the room-temperature trioctylphosphine oxide/PbBr₂ method. Despite photoluminescence quantum yields nearing 100%, these spheroidal quantum dots exhibit an elongated red photoluminescence tail not observed in typical cubic quantum dots synthesized via hot injection. We explore the origins of this elongated red tail through structural and optical characterization including small-angle X-ray scattering, transmission electron microscopy and time-resolved, steady-state, and single quantum dot photoluminescence. From these measurements we conclude that the red tail originates from emissive traps. We show that treating spheroidal quantum dots with phenethylammonium bromide decreases the line shape asymmetry and increases passivation–consistent with emissive traps due to polar facets.This work, and the roles of J.K., S.G., B.F.H, R.M., D.M.L., J.N.P., M.F.T., M.P., S.Y., G.D. and D.S.G were primarily supported by the National Science Foundation under the STC IMOD Grant (No. DMR2019444). B.F.H. and D.M.L. acknowledge support from the National Science Foundation through the Graduate Research Fellowship Program (NSF-GRFP) under Grant No. DGE 2040434. R.J.E.W. carried out streak camera measurements and was supported by the Office of Naval Research (ONR N000-14-20- 1-2191) and the Momental Foundation via the Mistletoe Fellowship. The authors acknowledge the use of facilities and instruments at the Photonics Research Center (PRC) at the Department of Chemistry, University of Washington, as well as that at the Research Training Testbed (RTT), part of the Washington Clean Energy Testbeds system. Part of this work was carried out at the Molecular Analysis Facility, a National Nanotechnology Coordinated Infrastructure site at the University of Washington which is supported in part by the National Science Foundation (NNCI-1542101), the Molecular Engineering & Sciences Institute, and the Clean Energy Institute. TEM was carried out at the Facility for Electron Microscopy of Materials at the University of Colorado Boulder (CU FEMM, RRID: SCR_019306). J.K. acknowledges David M. Jonas (professor, University of Colorado Boulder) for discussion regarding potential causes of an elongated red photoluminescence tail in quantum dots. D.M.L. acknowledges use of the SasView application for fitting SAXS data. SasView was originally developed under NSF award DMR-0520547 and contains code developed with funding from the European Union’s Horizon 2020 research and innovation program under the SINE2020 project, grant agreement No 654000. B.F.H. acknowledges Olivia F. Bird (graduate student, University of Colorado Boulder) and Sophia M. Click (postdoctoral researcher, University of Colorado Boulder) for discussions related to TEM image segmentation and size analysis using Trainable Weka Segmentation in ImageJ.https://pubs.acs.org/doi/full/10.1021/acs.nanolett.4c0499