**1. Introduction**

Various organic-inorganic hybrid solar cells with perovskite-type pigments have been broadly studied recently [1–4]. Organic solar cells with a CH3NH3PbI3 compound that has a perovskite structure have high conversion efficiencies [5–7]. Since achieving a photoconversion efficiency of 15% [8], higher efficiencies have been reported for various device structures and processes [9–11], and the photoconversion efficiency increased up to ca. 20% [12–18]. The solar cell properties depend on the crystal structures of the perovskite phase, electron transport layers, hole transport layers (HTLs), nanoporous layers, and fabrication process. Especially, the energy band gaps and carrier transport of the perovskite compounds are dependent on the crystal structures [19], and further analyses of the structures and properties are imperative.

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

In this article, fabrication and characterization of perovskite-type solar cells are reviewed and summarized. Various perovskite compounds, such as CH3NH3PbI3, [HC(NH2)2]PbI3, and CsSnI3, are expected for solar cell materials. Since these perovskite-type materials often have nanostructures in the solar cell devices, information on the crystal structures, fabrication, and characterization would be useful for fabrication of the perovskite-type crystals. Transmission electron microscopy, electron diffraction, and high-resolution electron microscopy are powerful tools for structure analysis of solar cells [20] and perovskite-type structures in atomic scale [21–23].

The crystals of CH3NH3PbX3 (X = Cl, Br, or I) have perovskite structures and provide structural transitions upon heating [24–26]. The crystal structures of cubic, tetragonal, and orthorhombic CH3NH3PbI3 are shown in **Figure 1(a)**–**(c)**, respectively. Space group is *Pm*-3*m*, and the lattice constant *a* = 6.391 Å at 330 K for cubic CH3NH3PbI3 [27]. Hydrogen positions in the orthorhombic CH3NH3PbI3 were also determined at 4 K by neutron diffraction [28], as shown in **Figure 1(d)**. Although the crystals of perovskite CH3NH3PbX3 provide a cubic system as the high-temperature phase, the CH3NH3 <sup>+</sup> ions are polar and have a symmetry of C3v. This results in formation of cubic phase with disordering [27]. Besides the CH3NH3 + ions, disordering of the halogen ions is also observed in the cubic perovskite phase, as indicated in **Figure 1(a)**. Site occupancies of I were 1/4, and those of C and N were 1/12, respectively. The CH3NH3 ion occupies 12 equivalent orientations of the C2 axis, and hydrogen atoms have two kinds of configurations on the C2 axis. Therefore, the total degree of freedom is 24 [26].

**Figure 1.** Structure models of CH3NH3PbI3 with (a) cubic, (b) tetragonal and (c) orthorhombic structures, and (d) orthorhombic CH3NH3PbI3 with hydrogen positions.

In addition to the CH3NH3PbI3 (MAPbI3), [HC(NH2)2]PbI3 (formamidinium lead iodide, FAPbI3) provided high conversion efficiencies [17, 18]. Structure parameters, including hydrogen positions, were also determined at 298 K by neutron diffraction [29], and the structure model with the lattice constant *a* = 6.3620 Å is shown in **Figure 2(a)**.

**Figure 2.** Structure models of (a) [HC(NH2)2]PbI3, (b) CsSnI3, and (c) CsGeI3 with cubic structures.

CH3NH3 ions can be substituted by other elements such as Cs. The structure models of CsSnI3 and CsGeI3 for high-temperature phase are shown in **Figure 2(b)** and **(c)**, respectively [30–32]. Space group is *Pm*-3*m* (Z = 1), and *a* = 6.219 Å at 446 K for CsSnI3, *a* = 6.05 Å at 573 K for CsGeI3, respectively. Solar cells with F-doped CsSnI2.95F0.05 provided a photoconversion efficiency of 8.5% [6].
