Structural chemistry of layered lead halide perovskites containing single octahedral layers.

Jason A Mcnulty,Philip Lightfoot

doi:10.1107/s2052252521005418

Abstract

We present a comprehensive review of the structural chemistry of hybrid lead halides of stoichiometry APbX 4, A 2PbX4 or A A'PbX 4, where A and A' are organic ammonium cations and X = Cl, Br or I. These compounds may be considered as layered perovskites, containing isolated, infinite layers of corner-sharing PbX 4 octahedra separated by the organic species. First, over 250 crystal structures were extracted from the CCDC and classified in terms of unit-cell metrics and crystal symmetry. Symmetry mode analysis was then used to identify the nature of key structural distortions of the [PbX 4]∞ layers. Two generic types of distortion are prevalent in this family: tilting of the octahedral units and shifts of the inorganic layers relative to each other. Although the octahedral tilting modes are well known in the crystallography of purely inorganic perovskites, the additional layer-shift modes are shown to enormously enrich the structural options available in layered hybrid perovskites. Some examples and trends are discussed in more detail in order to show how the nature of the interlayer organic species can influence the overall structural architecture; although the main aim of the paper is to encourage workers in the field to make use of the systematic crystallographic methods used here to further understand and rationalize their own compounds, and perhaps to be able to design-in particular structural features in future work.

Highlights

Lead halide perovskites (LHPs) have recently revolutionized the field of solar cells, in addition to showing novel and promising properties in several other areas, such as luminescence, ferroelectricity etc. (Green et al, 2014; Smith et al, 2019; Zhang, Song, Cheng et al, 2020)
Octahedral tilting and layer shifts are shown to be the key distortion modes underlying the nature of the inorganic perovskite-like layers in this family of materials. The complexity of these systems goes far beyond the octahedral tilt systems traditionally seen in purely inorganic layered perovskites
First and foremost, we use our analysis to show the relationships between apparently diverse groups of structures and compositions, by classifying in terms of unit-cell metrics and key distortion modes, relative to idealized parent phases

Summary

Introduction

Lead halide perovskites (LHPs) have recently revolutionized the field of solar cells, in addition to showing novel and promising properties in several other areas, such as luminescence, ferroelectricity etc. (Green et al, 2014; Smith et al, 2019; Zhang, Song, Cheng et al, 2020). Even within this sub-field there are well over 250 crystal structures reported in the Cambridge Crystallographic Database (census date 11/11/20). The use of the phrase ‘layered perovskite’ in the present work corresponds to the personal opinions and preferences of the authors and it is not intended to impose on other authors

Octahedral tilting and symmetry mode analysis

Layered perovskites

Hybrid layered perovskites

More complex derivatives

Polymorphs and phase transitions

Summary and conclusions