Tunable Perovskite Semiconductor CH3NH3SnX3 (X: Cl, Br, or I) Characterized by X-ray and DTA

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Abstract
A series of perovskite halide solid solutions was synthesized and characterized by DTA and X-ray diffraction. The solid solution CH3NH3SnBr3-xClx (x = 0-3) changes its color from red, orange, yellow to a colorless state with increasing x. Although each highest temperature phase belongs to a cubic system, a slight trigonal distortion was observed above x = 1.0 at room temperature. Similar continuous solid solutions with black colors were confirmed for CH3NH3SnBr3-xIx (x = 0, 1, 2, and 3) keeping a cubic perovskite structure over the whole x region. On the other hand, continuous solid solutions CH(3)NH(3)Snl(3-x)Cl(x) could not be confirmed. The solid-state static H-1 NMR suggested that the isotropic reorientation of the cation does not freeze even at 150 K for the perovskite having a large anionic sublattice. The characteristic changes of the color and the electric structure for these perovskites were discussed analytically on the basis of the tight-binding approach. This simple one-dimensional expression predicts that the tin(II) perovskite halide is a direct band gap semiconductor with tailorable properties.