Affiliation:
1. Dipartimento di Scienza e Alta Tecnologia & To.Sca.Lab Università dell’Insubria 22100 Como Italy
2. Photon Science Division Laboratory for Synchrotron Radiation - Condensed Matter Paul Scherrer Institut 5232 Villigen Switzerland
3. Institute of Inorganic Chemistry Department of Chemistry and Applied Biosciences ETH Zürich CH-8093 Zürich Switzerland
4. Laboratory for Thin Films and Photovoltaics Empa-Swiss Federal Laboratories for Materials Science and Technology CH-8600 Dübendorf Switzerland
5. Istituto di Cristallografia & To.Sca.Lab Consiglio Nazionale delle Ricerche 22100 Como Italy
Abstract
Lead halide perovskite nanocrystals (NCs) have emerged as next‐generation semiconductors capable of unifying superior photoemission properties, facile and inexpensive preparation, compositional and structural versatility. Among them, CsPbBr3 is a model system in theoretical and experimental studies owing to its intrinsic chemical stability. Nonetheless, knowledge of the precise magnitude and the size‐ and temperature‐dependent lattice and structural distortions is lacking, and the static/dynamic nature of disorder in NCs remains an open question. Herein, robust reciprocal space X‐ray total scattering analysis is applied and accurate lattice distortions, PbBr bond distances, and PbBrPb angles versus NCs size are extracted. The lattice anisotropy increases upon expansion on downsizing while, upon contraction on cooling, the lattice distortion behaves differently at intermediate (9 nm) and ultrasmall (5 nm) sizes and from the bulk. Bond distances (stretched by ≈1%) do not show any size dependence, whereas equatorial and axial angles denote more symmetric octahedral arrangements in the smallest sizes, where they differ by ≈2° compared to ≈8° in the bulk. Anomalously high atomic displacement parameters of axial bromine ions persisting down to cryogenic temperatures suggest statically disordered octahedral tilts. These results provide insights having important implications on size‐dependent emission properties and the exciton fine structure.
Funder
Ministero dell’Istruzione, dell’Università e della Ricerca
Fondazione Cariplo
Horizon 2020 Framework Programme
Subject
General Earth and Planetary Sciences,General Environmental Science