Proceedings of Online nanoGe Fall Meeting 20 (OnlineNFM20)
Publication date: 4th October 2020
Unlike typical inorganic semiconductors, lead–halide perovskites (LHPs) exhibit significant ionic conductivity, which is believed to affect their performance and stability. Motivated by a recent experimental study that suggested pressure as a means to control ionic conductivity in CsPbBr3 [1], we present a detailed theoretical study of the atomic scale effects of pressure on anion migration in the low temperature orthorhombic Pnma phase of CsPbBr3. Using nudged elastic band calculations based on density functional theory, we compute all symmetrically inequivalent activation barriers for anion migration to their closest neighbours, as a function of hydrostatic pressure in the range 0.0–2.0 GPa. We then use those values as parameters in a kinetic model which allows us to connect the atomic scale calculations to the macroscopic anion mobility tensor as a function of applied pressure.
We find that the mobility is enhanced by pressure in the plane spanned by the [100] and [001] lattice directions, while along the [010] direction it is diminished, leading to an effective 3D-to-2D transition of the mobility at elevated pressures. This can be explained by the fact that a network of only a few symmetrically inequivalent paths dominates the mobility at elevated pressures. Our results demonstrate the significant influence of pressure on both the rate and direction of anion migration in CsPbBr3, which we consider likely to hold for other LHPs.
We acknowledge funding from the European Union’s Horizon 2020 MSCA Innovative Training Network under grant agreement number 764787, and the Energy oriented Centre of Excellence (EoCoE-II), grant agreement number 676629. This research made use of the Balena High Performance Computing (HPC) Service at the University of Bath. Calculations were performed on the GW4 Isambard HPC, and the SuperMUC-NG HPC through PRACE. We thank Dr. William Saunders for valuable feedback.
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