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Thomas Young Centre - TYC@Imperial: Low-Energy Polar Domain Walls in Halide Perovskites

Image: Figure 1
Figure 1

Date: 11 March 2019   Time: 12:00 - 13:00

Low-Energy Polar Domain Walls in Halide Perovskites presented by Andrew Warwick.

Abstract:
The perovskite methyl ammonium lead iodide (MAPbI­­­­3) has recently attracted significant interest (1) in the photovoltaic community owing to its promising power conversion efficiencies, rapidly growing upwards of 23.7% (2), surpassing that of some existing silicon-based devices. Despite this interest, there are still some open questions regarding the physical properties of MAPbI3, such as the role of ferroelastic domain walls which appear in abundance (3). In domain walls emergent functionalities can appear due to the change of structure at the interface.

Here, we present density functional theory simulations of domain walls in the inorganic analogue caesium lead iodide, CsPbI3, which serves as a starting point towards simulating the more structurally complex MAPbI3 (4). There are two types of ferroelastic walls (5) which we find to act as electron and hole sinks respectively. Furthermore, we calculate the walls in CsPbI3 to be strongly polar, very thin and, in agreement with their experimental observation in MAPbI3, likely to have low formation energies(3). The emergent polarity at these walls could be part of the origin of MAPbI3’s high power conversion efficiency and/or be engineered to enhance it due to the photoferroic effect.

Figure 1. The two types of ferroelastic wall in MAPbI3 calculated to be electron or hole sinks with an in-plane polarization. Green arrows denote the order parameter direction and dashed black lines indicate the wall plane. A proposal for improving charge carrier mobility and delaying recombination rates is shown in this schematic.


References
[1] Li W. et al. Nat. Rev. Mater. (2017), 2, 16099

[2] National Renewable Energy Laboratory. Best Research-Cell Efficiencies Chart https://www.nrel.gov/pv/ (2019) Accessed March 4th, 2019

[3] Rothmann M. et al. Nat. Commun. (2017), 8, 14547

[4] Warwick A. et al. arXiv preprint arXiv:1901.00704 (2019)

[5] Schiaffino A. and Stengel M., Phys. Rev. Lett. 199, 137601 (2017)

Location:  Room G01, Royal School of Mines, Imperial College London