Effective Ion Mobility and Long-Time Dark Current of Metal-Halide Perovskites of Different Crystallinity and Composition

TL;DR

This study investigates ion transport and dark current stability in different metal-halide perovskites, revealing composition-dependent ion mobility and its impact on device performance and degradation over long timescales.

Contribution

It provides new insights into the ion mobility behavior in MAPbBr3 and MAPbI3 perovskites, highlighting the influence of composition and crystallinity on ion transport and dark current evolution.

Findings

Ion current reaches steady state within 10-10,000 seconds depending on bias.

Ion mobility varies with electric field and composition, with MAPbBr3 showing field-enhancement.

MAPbBr3 exhibits slower defect drift compared to MAPbI3.

Abstract

Ion transport properties in metal-halide perovskite still constitute a subject of intense research because of the evident connection between mobile defects and device performance and operation degradation. In the specific case of X-ray detectors, dark current level and instability is regarded to be connected to the ion migration upon bias application. Different compositions (MAPbBr3 and MAPbI3) and structures (single- and micro-crystalline) are checked by the analysis of long-time dark current evolution. In all cases, electronic current increases with time before reaching a steady-state value within a response time (from 10.000 s down to 10 s) that strongly depends on the applied bias. Our findings corroborate the existence of a coupling between electronic transport and ion kinetics that ultimately establishes the time scale of electronic current. Effective ion mobility mui is extracted that exhibits applied electrical field E dependence that varies on the perovskite composition. While ion mobility results field-independent in the case of MAPbI3, a clear field-enhancement is observed for MAPbBr3 (dmui/dE>0), irrespective of the crystallinity. Both perovskite compounds present effective ion mobility in the range of mui = 10-7-10-6 cm-2 V-1 s-1, in accordance with previous analyses. The E-dependence of the ion mobility is related to the lower ionic concentration of the bromide compound. Slower-migrating defect drift is suppressed in the case of MAPbBr3, in opposition to that observed here for MAPbI3.