Planar defects and dynamic disorder in lead halide perovskite nanocrystals unveiled through reciprocal space total scattering methods
Federica Bertolotti a, Anna Vivani a, Loredana Protesescu b, Georgian Nedelcu b, Maksym V. Kovalenko b, Norberto Masciocchi a, Antonietta Guagliardi c
a University of Insubria and To.Sca.Lab, Como, Italy
b ETH-Zürich and EMPA, Zürich, Switzerland
c Istituto di Cristallografia, CNR, and and To.Sca.Lab, Como, Italy
Proceedings of Atomic-level characterization of hybrid perovskites (HPATOM)
Online, Spain, 2021 January 26th - 28th
Organizers: Dominik Kubicki and Amita Ummadisingu
Oral, Federica Bertolotti, presentation 010
Publication date: 14th January 2021

Lead halide perovskites (LHP) are long-known crystalline materials with ABX3 general formula, characterized by a three-dimensional interconnection of [PbX6]4- octahedra and a large A cation residing the cuboctahedra cavities in between. These materials in form of nanocrystals (NCs) are considered ideal candidates for many optoelectronic applications.[1] Due to the dynamic nature of the perovskite lattice preventing the charge carriers from trapping, LHP NCs are highly tolerant to structural defects and surface states that are considered benign with respect to their electronic and optical properties.[2]

The flexible nature of the perovskite framework, very prone to structural defectiveness, coupled with the reduced size of the crystalline domains, makes these materials unsuitable for conventional crystallographic methods, unable to properly account for deviations from ideally infinite periodic structures. At this purpose total scattering techniques based on the Debye Scattering Equation (DSE), considering both Bragg and diffuse scattering on equal foot, have been established as effective methods for characterizing nanoscale materials and taking into account size-induced structural defects emerging with downsizing.[3] Through the DSE-based method developed by some of us,[4] starting from real space atomistic models, structural (intended both as periodic crystal structure and structural defectiveness or disorder) and microstructural information on NCs can be simultaneously derived within a unified approach, with all the well-known advantages associated to the use of reciprocal space methods.

Using newly developed defective models within the DSE-based approach, we were able to unveil the presence of locally ordered subdomains in all-inorganic LHP (CsPbX3) NCs, characterized by the orthorhombic tilting of the [PbX6]4- octahedra.[5] These subdomains are hinged together by a network of two-dimensional twin boundaries, through which the coherent arrangement of Pb2+ ions is nearly preserved. The density of these twin boundaries, migrating trough the particles via cooperative rotations of the octahedra, determines the size of the subdomains and increases upon temperature increase, due to the entropic stabilization of the polyfragmented NCs. These synchronized movements modify the domains sizes and orientations, leading to an “apparent” higher crystal symmetry (tetragonal or cubic) on average, while keeping locally (at the subdomains scale) the tilted “orthorhombic” arrangement of the octahedra.

Beyond CsPbBr3 NCs, this advanced model was also applied to six-monolayer thick nanoplatelets providing robust morphological and structural information, in particular on the orientation of the orthorhombic structure with respect to their peculiar morphology. Fundamental insights on nanoplatelets surface termination were also derived.[6]

© Fundació Scito
We use our own and third party cookies for analysing and measuring usage of our website to improve our services. If you continue browsing, we consider accepting its use. You can check our Cookies Policy in which you will also find how to configure your web browser for the use of cookies. More info