Crystal structures of various perovskite halide compounds expected as solar cell materials

The crystal structures of various types of perovskite halide compounds expected for solar cells were summarized and described. Atomic arrangements of these perovskite compounds can be investigated by X-ray diffraction and transmission electron microscopy. Based on the structural models, X-ray diffractions were calculated and discussed. Other halides such as elemental substituted or cation ordered double perovskite compounds were also described. In addition to the ordinary 3-dimensional perovskites, low dimensional perovskites with 2-, 1-, or 0-dimensionalities were summarized. The structural stabilities of the perovskite halides could be investigated by calculating the tolerance and octahedral factors, which can be useful for the guideline of elemental substitution to improve the structures and properties, and several low toxic halides were proposed. For the device conformation, highly crystalline-orientated grains and dendritic structures can be formed and affected the photovoltaic properties. The actual crystal structures of perovskite halides in the thin film configuration can be investigated by Rietveld analysis optimizing the atomic coordinates and occupancies. These results are useful for structure analysis of perovskite halide crystals, which are expected to be next-generation solar cell materials.