Nonlinear ion mobility at high electric field strengths in the perovskites SrTiO3 and CH3NH3PbI3

D Kemp and RA De Souza, PHYSICAL REVIEW MATERIALS, 5, 105401 (2021).

DOI: 10.1103/PhysRevMaterials.5.105401

As the characteristic dimensions of perovskite devices shrink to the nanoscale, operating voltages of a few volts lead to huge field strengths and, consequently, to the possibility of field-enhanced ion mobility. In this paper, the electrochemical mobility of X anions (u(X)) along < 100 > in the ABX(3) perovskite structure was investigated as a function of electric field strength E and temperature T by means of classical molecular dynamics simulations. Two different cases were examined: one representative of inorganic perovskites, oxide-ion mobility (u(O)) in cubic SrTiO3; and the other representative of hybrid inorganic-organic perovskites, iodide-ion mobility (u(I)) in cubic CH3NH3PbI3. In both cases, isothermal mobilities are, as expected, independent of field at low values (E < 10(0) MV cm(-1)) but become field dependent at higher values. Data obtained for u(O)(E, T) can be described quantitatively with an analytical treatment incorporating a modified Haven ratio for a dilute solution. In contrast, u(I)(E, T) displays complex behavior. At high fields, the degree of field enhancement is underestimated by the analytical treatment, while in the field-independent regime, the data imply that moderate fields decrease u(I). Our study thus demonstrates that for cubic, inorganic ABX(3) perovskites u(X) (E, T) along < 100 > can now be predicted quantitatively, but for hybrid perovskites substantially more complex models are required.

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