3D-to-2D Transition of Anion Vacancy Mobility in CsPbBr₃ under Hydrostatic Pressure

Abstract

Anion vacancy migration in the orthorhombic Pnma phase of the lead−halide perovskite CsPbBr 3 under hydrostatic pressure is studied computationally. Density functional theory calculations are used to determine transition states, activation enthalpies, and attempt frequencies for vacancies to hop between nearby lattice sites, under pressure in the range 0.0− 2.0 GPa. The resulting data are used to parametrize a kinetic model of vacancy migration under the influence of an electric field, which is solved in the steady state to determine the anion vacancy mobility tensor as a function of pressure. It is found that the mobility tensor becomes increasingly anisotropic with increasing pressure, such that at 2.0 GPa, the mobility within the (010) lattice plane is 3 orders of magnitude greater than the mobility normal to it. The results demonstrate the potentially significant influence of pressure, and by extension, other forms of stress, on defect migration in lead−halide perovskites.

Factors influencing halide vacancy transport in perovskite solar cells

“…Similar slopes are found in each case, but some non-linearities appear owing to the compounding of electrostatic and steric factors. We note that similar barrier heights have been reported by by Smolders et al [54]. for CsPbBr 3 , but a distinct change in anistropic diffusion behaviour was predicted above 1 GPa due to static octahedral tilting patterns that emerge.…”

“…Moreover, rather than being fixed, strain has been found to evolve under visible light illumination [52,53]. While the understanding of strain distributions for crystals and films continues to evolve in the community, we note that the effect of pure hydrostatic pressure has been experimentally probed for a range of metal halide perovskites [37,54].…”

Design‐Dependent Switching Mechanisms of Schottky‐Barrier‐Modulated Memristors based on 2D Semiconductor

“…Therefore, the total number of conducting electrons of TMDC can be roughly estimated as 10 9 . On the other hand, the ratio of defect mobility [ 36 ] and electron mobility [ 37 ] can vary from 10 –1 to 10 –6 , depending on the type of materials, as well as the type of defects. As a result, the value of E is normally in the range of 10 4 to 10 9 C –1 , where E = 10 4 C −1 corresponds to a small mobility ratio (≈10 –6 ) while E = 10 9 C −1 corresponds to a large mobility ratio (≈10 –1 ).…”

Diffusivity Tensors of Br and Cs Vacancies in Biaxially Strained Perovskite CsPbBr3

“…The nonuniform changes in activation energies were found to lead to a decrease in the vacancy mobility in the [010] direction, but an increase in the directions perpendicular to it, with increasing pressure. 14 The anisotropic response of ion-vacancy transport to an isotropic stress (hydrostatic pressure) indicates not only that the relationship between stress/strain and ion-vacancy transport is not straightforward in general, but also that the particular perovskite phase plays a significant role in determining those relationships, both of which points appear to be underappreciated in the literature. Furthermore, the available data indicate that, for the cesium−lead−halides, the stable perovskite structure, until well above room temperature, is the orthorhombic Pnma structure 16−23 (we note that it may not be thermodynamically stable overall in all cases, e.g., due to transformation to a nonperovskite structure in the case of CsPbI 3 24 ).…”