Abstract
In this thesis, we will report on an investigation of how the organo-halide perovskite solar cell, thin-film materials of varied halide content, MAPbI3, MAPbI2Br, MAPbIBr2, MAPbBr3, behave under the applied electrical field and under different controlled environments of dry and moist nitrogen atmosphere. The morphology of the film of different length scale was examined with optical microscope (OM) and atomic force microscope (AFM). The chemical composition of the films was measured with X-ray photoemission spectroscopy (XPS) with particular emphasis given to I 3d, Pb 4f, and Br 3d because of the known migration of ionic species that is enhanced under the influence of electrical field and accelerated decomposition in moist environment. One dimensional XPS imaging was also used to map out the distribution of ionic species across the electrodes. Our results show that the iodide migration among four types of perovskite films, as vividly demonstrated with moving traces in OM, varies with the I/Br ratio and the environment where the electrical field was applied. Higher bromide content and dry environment can significantly retard the halide migration, due to the enhanced stability contributed by bromide ions.