Proceedings of September Meeting 2016 (NFM16)
Publication date: 14th June 2016
Despite the emergence as a promising opto-electronic material, the fundamental physics in organic-inorganic metal-halide perovskite (e.g. CH3NH3PbI3-xClx, CH3NH3PbI3), is still not sufficiently understood. Among them, the origin of hysteresis in the current-voltage (J-V) curves, i.e. the sweeping-history-dependent electrical current, is one of the most important topics. To investigate the mechanism, we employ different methods that help to identify the origin and effect of ion migration. In detail we use electroabsorption (EA) spectroscopy, a non-invasive in-situ characterization approach, to explore the built-in potential (VBI) in working photovoltaic devices. Furthermore, we study the temperature dependent J-V behavior. The electrical current relaxation process provides the activation energy of the ionic migration. In order to investigate the nature of these ions, we further perform X-ray photoemission spectroscopy (XPS) experiments, showing the redistribution of iodine after applying a constant electrical bias in a laterally-configured structure device. In addition, we carry out fluorescence microscopy under an electrical field which allows us to directly track the migration and accumulation of ions. This experiment allows to study the dynamic process of – in this case - iodide ions under an external electrical field, and estimate the mobility and diffusion constant of these ions. We associate the migration/accumulation of iodide ions with the modulation of interfacial barrier between perovskite and electrodes, though a degradation of the perovskite – especially at higher biases - may become prevalent as well. This change of interface gives rise to the shift of built-in potential, resulting in the observation of hysteresis in J-V curves. Furthermore we investigate the influence of PCBM on the migration of ions, which appears to be impeded by the presence of interdiffused PCBM molecules.
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