Understanding lead iodide perovskite hysteresis and degradation causes by extensive electrical characterization

We studied the hysteresis and electric field effects on planar CH3NH3PbI3 perovskite devices, synthetized from laser-ablated precursors, by means of electrical characterizations at different scan rates and optical measurements. The aim of our investigation is to characterize the phenomena behind perovskite degradation under prolonged applied electric field. Using a perovskite more resistant to electric field induced degradation, we run long time characterizations that were not accomplishable before. Thus, we distinguished all the degradation involved phenomena. The results point to the presence of ions migrating in the perovskite when the device is biased. Our data showed that ion migration degrades the interfaces with the consequent creation of degradation layers that limit the current injected in the device and the extracted photocurrent. These layers where detected also by means of optical Raman characterization. In order to explain the details of the mechanisms concurring to the observed behaviors, we presented a qualitative model. The observed phenomena exacerbated by the planar structure are even more destructive on standard solution processed perovskites to which the results of this work can be extended. Since, the same degradation dynamics occur on vertical devices, typical on perovskite solar cells, this work provides a useful in-depth analysis of the ionic migration effects.