Correlative Imaging of Individual CsPbBr3 Nanocrystals: Role of Isolated Grains in Photoluminescence of Perovskite Polycrystalline Thin Films

We report on the optical properties of a CsPbBr3 polycrystallinethin film on a single grain level. A sample composed of isolated nanocrystals(NCs) mimicking the properties of the polycrystalline thin film grainsthat can be individually probed by photoluminescence spectroscopywas prepared. These NCs were analyzed using correlative microscopyallowing the examination of structural, chemical, and optical propertiesfrom identical sites. Our results show that the stoichiometry of theCsPbBr(3) NCs is uniform and independent of the NCs'morphology. The photoluminescence (PL) peak emission wavelength isslightly dependent on the dimensions of NCs, with a blue shift upto 9 nm for the smallest analyzed NCs. The magnitude of theblueshift is smaller than the emission line width, thus detectableonly by high-resolution PL mapping. By comparing the emission energiesobtained from the experiment and a rigorous effective mass model,we can fully attribute the observed variations to the size-dependentquantum confinement effect.