**6. Other compounds with perovskite structures for solar cells**

In addition to CH3NH3PbX3 (X=Cl, Br, or I) compounds, various perovskite compounds with perovskite structures for solar cells have benn reported and summarized [1]. Crystal systems and temperatures of CsSnI3 are listed in Table 12, which has very similar structures and phase transitions [3] compared with the CH3NH3PbX3. Solar cells with F-doped CsSnI2.95F0.05 provided an photo-conversion efficiency of 8.5% [4].


**Table 12.** Crystal systems and temperatures of CsSnI3.

**000**

**c d**

**000**

**112**

**112**

**200**

**002**

**Figure 10.** Calculated electron diffraction patterns of tetragonal CH3NH3PbI3 along (a) [001], (b) [100], (c) [021], (d)

**000**

**110 112**

**000**

**000**

**110**

**020**

**114**

**204**

**022**

**002**

**b**

**200**

**a**

96 Solar Cells - New Approaches and Reviews

**e**

[221] and (e) [110].

**110 110**


**Table 13.** Crystal systems and temperatures of CH3NH3GeCl3.

Similar structures of CH3NH3GeCl3 and CH3NH3SnCl3 are shown in Table 13 and 14, respec‐ tively [28, 26]. Ion radii of Ge and Sn ions are listed in Table 8, and they can be substituted for the Pb atoms in CH3NH3PbX3. Lead-free CH3NH3SnI3 solar cells were developed, which provided 5.7% efficiency [7]. (CH3CH2NH3)PbI3 with a 2H perovskite structure was reported, which privided 2.4% efficiency [9]. Perovskite oxides such as [KNbO3]0.9[BaNi0.5Nb0.5O3-x]0.1 were found to have an energy gap of ~1.4 eV, which would also be expected as solar cell materials [5].


**Table 14.** Crystal systems and temperatures of CH3NH3SnCl3.
