Long-Term Field Screening by Mobile Ions in Thick Metal Halide Perovskites: Understanding Saturation Currents

Abstract

Metal halide perovskite-based semiconductor devices with micrometer-to-millimeter-thick perovskite layers show a current response upon polarization which evolves up to several hours, transiting several regimes. This is the case of X-ray detectors where the use of absorber perovskites produces instabilities in the dark reverse saturation current hindering the signal processing. Even though these phenomena are often attributed to the electronic-ionic conductivity and the interface phenomena in these perovskites, a proper theoretical description is missing. Herein, the numerical simulation study reproduces the main experimental trends and explains the origin of some of the apparently-always-increasing current transients in thick perovskite samples. The mobile ion concentration and mobility are correlated with three main transport regimes and interpretation and parameterization are provided to the current saturation time in terms of the ionic screening of the electric field toward the interfaces. The final steady-state under reverse polarization is found as diffusion-limited electronic current, which results from abrupt mobile ion depletion proportional to the Debye length in the vicinity of a contact. The conclusions suggest the material optimization of the contact interfaces as a pathway to reduce the long current saturation times in these devices.