Abstract
We report Atomic Force Microscopy (AFM) and Scanning Kelvin Probe Microscopy (SKPM) studies on the surface morphology and surface potential properties of CH3NH3PbI3, CH3NH3PbI3-xClx, CH3NH3PbI3-xBrx and CH3NH3PbBr3-xClx, respectively. For CH3NH3PbI3 rod structure, its surface potential is independent of the precursor concentration, suggesting a robust electronic feature. Surface potential studies of CH3NH3PbI3 particle reveal that the Fermi level within CH3NH3PbI3 is strongly influenced by the substrate. In the case of CH3NH3PbI3-xClx, its surface potential depends on precursor concentrations and we suspect that chlorine concentrated solutions might lead to more chlorine incorporation in the final products, thus lowering its Fermi level. Also, we studied the surface potentials of CH3NH3PbI3-xBrx and CH3NH3PbBr3-xClxwith specified halide ratios. The surface potential differences between different samples are related to their work function variations. These results are helpful to the understanding of the structural and electronic properties of perovskite materials.
Highlights
Since their first introduction in solar cells in 2009,1 methylammonium lead halide perovskite materials (e.g., CH3NH3PbX3,X = Cl, Br, I) have attracted much attention in photovoltaic research community.[2,3,4,5,6,7,8,9] The power conversion efficiency of perovskite based solar cells has already surpassed 20% in a few years.[10]
We studied the surface potential of I/Br and Br/Cl mixed perovskites with specified ratios and the surface potential is correlated with their work functions
For rod perovskite deposited on n-type FTO substrate, it shows that when precursor concentration is decreased from 29 wt% to 4.8 wt%, the surface potential shows a little variations around 45 meV
Summary
For iodide/chloride mixed perovskite CH3NH3PbI3-xClx, a variety of experiments are conducted to investigate the role of chlorine element.[15,16,17,18,19,20,21,22,23,24,25] It shows that Cl ions in the precursor solution have a profound and beneficial effect on the film morphology,[15,16] carrier transport,[13] and stability,[17,26] even though Cl remains at a very low content in the perovskite lattice.[24,25,27,28] For iodide/bromide and chloride/bromide mixed perovskites, their optical and electronic properties can be tuned by changing the halide ratios.[29,30,31] These perovskites are mostly wide bandgap and are not suitable for photovoltaic applications due to their transparency to most of the solar spectrum. We studied the surface potential of I/Br and Br/Cl mixed perovskites with specified ratios and the surface potential is correlated with their work functions
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