Effective Ion Mobility and Long-Term Dark Current of Metal Halide Perovskites with Different Crystallinities and Compositions

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 case of X-ray detectors, dark current level and instability are regarded to be connected to the ion migration upon bias application. Two compositions (MAPbBr(3) and MAPbI(3)) and structures (single- and microcrystalline) are checked by the analysis of long-term dark current evolution. Electronic current increases with time before reaching a steady-state value within a response time (from 104 down to 10 s) that strongly depends on the applied bias. A coupling between electronic transport and ion kinetics exists that ultimately establishes the time scale of electronic current. Effective ion mobility mu(i) is extracted for a range of applied electric field xi. While ion mobility results field- independent in the case of MAPbI(3), a clear field enhancement is observed for MAPbBr(3) (partial derivative mu(i)/partial derivative xi > 0), irrespective of the crystallinity. Both perovskite compounds present effective ion mobility in the range of mu(i) approximate to 10 (-7)-10(-6) cm(-2) V-1 s(-1), in accordance with previous analyses. The xi- 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 MAPbBr(3), in opposition to that observed here for MAPbI(3).

Automated summary

Ion transport properties in metal halide perovskite have a significant impact on device performance and operation degradation. In X-ray detectors, the dark current level and instability are related to ion migration. This study found that electronic current increases with time and reaches a steady-state value within a certain response time. There is a coupling between electronic transport and ion kinetics. The analysis of MAPbBr(3) suggests that ion mobility is affected by the electric field, while MAPbI(3) is unaffected.