Particle Ordering and A-site Composition Effects in Hybrid Organic-Inorganic Metal Halide Perovskite Quantum Dot Films

The promising optoelectronic properties of bulk metal halide perovskite semiconductors have motivated recent developments in nanoscale and quantum well perovskite congeners, including layered structures and nanocrystalline quantum dots (QDs). In addition to the ability to tune the optical bandgap and improve photoluminescence efficiency, confining the nanocrystalline dimensions has proven valuable in accessing compositions^[1] and crystallographic phases^[2] that are unstable in the bulk.
Herein, we report on structural studies of FA_xCs_1–xPbI₃ (FA = formamidinium) QD films by synchrotron X-ray scattering techniques. 15-nm FA_xCs_1–xPbI₃ QDs (x = 0, 0.1, 0.25, 0.5, 0.75, 1) were deposited from colloidal solution and investigated by grazing incidence wide-angle X-ray scattering (GIWAXS). GIWAXS patterns indicate coherent particle ordering on the substrate for thin spin-coated films, while the subsequent ligand exchange and particle depositions lead to isotropic ordering of the particles. The patterns also show evidence of crystallographic phase inhomogeneities and a transition from cubic (FAPbI₃) to tetragonal (Cs_0.5FA_0.5PbI₃) to orthorhombic (CsPbI₃) character in the composition series.
[1] A. Hazarika, et al., ACS Nano 2018, 12, 10327.
[2] A. Swarnkar, et al., Science 2016, 354, 92.