**1. Introduction**

Recently, organic-inorganic hybrid solar cells with perovskite-type pigments have been widely fabricated and rapidly studied [12, 8, 11]. Solar cells with a perovskite structure have high conversion efficiencies and stability as the organic solar cells. Since a photoconversion efficiency of 15% was achieved [2], higher efficiencies have been reported for various device structures and processes [13, 23], and the photoconversion efficiency was increased up to 19.3% [27]. The photovoltaic properties of solar cells are strongly dependent on the fabrication process, hole transport layers, electron transport layers, nanoporous layers, interfacial microstructures, and crystal structures of the perovskite compounds. Especially, the crystal structures of the perovskite-type compounds, strongly affect the electronic structures such as energy band gaps and carrier transport, and a detailed analysis of them is mandatory.

In the present article, crystal structures of perovskite-type compounds such as CH3NH3PbI3 CH3NH3PbCl3, CH3NH3PbBr3, CsSnI3, CH3NH3GeCl3, and CH3NH3SnCl3, are expected for solar cell materials, are reviewed and summarized. Since these perovskite-type materials often have nanostructures in the solar cell devices, summarized information on the crystal structures would be useful for structure analysis on the perovskite-type crystals. The nanostructures of the solar cell devices are often analysed by using X-ray diffraction (XRD) and transmission electron microscopy (TEM), and the diffraction conditions are investigated and summarized. Transmission electron microscopy, electron diffraction, and high-resolution electron micro‐ scopy are powerful tools for structure analysis of solar cells [18] and perovskite-type structures in atomic scale [17, 19].

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