Abstract
Focused-ion beam lift-out and annular milling is the most common method used for obtaining site specific specimens for atom probe tomography (APT) experiments and transmission electron microscopy. However, one of the main limitations of this technique comes from the structural damage as well as chemical degradation caused by the beam of high-energy ions. These aspects are especially critical in highly-sensitive specimens. In this regard, ion beam milling under cryogenic conditions has been an established technique for damage mitigation. Here, we implement a cryo-focused ion beam approach to prepare specimens for APT measurements from a quadruple cation perovskite-based solar cell device with 19.7% efficiency. As opposed to room temperature FIB milling we found that cryo-milling considerably improved APT results in terms of yield and composition measurement, i.e. halide loss, both related to less defects within the APT specimen. Based on our approach we discuss the prospects of reliable atom probe measurements of perovskite based solar cell materials. An insight into the field evaporation behavior of the organic-inorganic molecules that compose the perovskite material is also given with the aim of expanding the applicability of APT experiments towards nano-characterization of complex organo-metal materials.
Highlights
The uniqueness of atom probe tomography (APT) lies on its ability to analyze physical nanostructures and correlate them to the corresponding chemical information with sub-nanometer resolutions [1, 2]
Two notable characteristics of the films are immediately evident, as previously described in Ref. [26], and are important for the subsequent results obtained from the APT reconstructions: First, the perovskite layer is comprised of a polycrystalline structure with columnar grains of various sizes ranging from 50 nm to 400 nm (Fig 4)
This makes characterizing a grain boundary with APT challenging since the focused ion beam (FIB) lift-outs are randomly obtained and the diameter of the final needle-shaped specimens are considerably smaller than the grain sizes
Summary
The uniqueness of atom probe tomography (APT) lies on its ability to analyze physical nanostructures and correlate them to the corresponding chemical information with sub-nanometer resolutions [1, 2]. State-of-the-art specimen preparation techniques have made APT increasingly amenable to analyze the chemistry and structure of a wide range of advanced functional and structural materials ranging from multi-layer devices used in the photovoltaic industry to metallic glasses for diverse applications [1,2,3,4,5,6]. The evolution of laser-assisted APT has permitted the analysis of materials with semiconducting properties since specimen. Cryo-focused ion beam preparation of perovskite-based solar cells for atom probe tomography
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