Issue 8, 2017

Chemical tuning of dynamic cation off-centering in the cubic phases of hybrid tin and lead halide perovskites

Abstract

Hybrid halide perovskites combine ease of preparation and relatively abundant constituent elements with fascinating photophysical properties. Descriptions of the chemical and structural drivers of the remarkable properties have often focused on the potential role of the dynamic order/disorder of the molecular A-site cations. We reveal here a key aspect of the inorganic framework that potentially impacts the electronic, thermal, and dielectric properties. The temperature evolution of the X-ray pair distribution functions of hybrid perovskites ABX3 [A+ = CH3NH3 (MA) or CH(NH2)2 (FA); B2+ = Sn or Pb; X = Br, or I] in their cubic phases above 300 K reveals temperature-activated displacement (off-centering) of the divalent group 14 cations from their nominal, centered sites. This symmetry-lowering distortion phenomenon, previously dubbed emphanisis in the context of compounds such as PbTe, is attributed to Sn2+ and Pb2+ lone pair stereochemistry. Of the materials studied here, the largest displacements from the center of the octahedral sites are found in tin iodides, a more moderate effect is found in lead bromides, and the weakest effect is seen in lead iodides. The A-site cation appears to play a role as well, with the larger FA resulting in greater off-centering for both Sn2+ and Pb2+. Dynamic off-centering, which is concealed within the framework of traditional Bragg crystallography, is proposed to play a key role in the remarkable defect-tolerant nature of transport in these semiconductors via its effect on the polarizability of the lattice. The results suggest a novel chemical design principle for future materials discovery.

Graphical abstract: Chemical tuning of dynamic cation off-centering in the cubic phases of hybrid tin and lead halide perovskites

Supplementary files

Article information

Article type
Edge Article
Submitted
30 Mar 2017
Accepted
31 May 2017
First published
16 Jun 2017
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2017,8, 5628-5635

Chemical tuning of dynamic cation off-centering in the cubic phases of hybrid tin and lead halide perovskites

G. Laurita, D. H. Fabini, C. C. Stoumpos, M. G. Kanatzidis and R. Seshadri, Chem. Sci., 2017, 8, 5628 DOI: 10.1039/C7SC01429E

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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