Controlled Reduction of Sn(4+) in the Complex Iodide Cs(2)SnI(6) with Metallic Gallium

Metal gallium as a low-melting solid was applied in a mixture with elemental iodine to substitute tin(IV) in a promising light-harvesting phase of Cs(2)SnI(6) by a reactive sintering method. The reducing power of gallium was applied to influence the optoelectronic properties of the Cs(2)SnI(6) phase via partial reduction of tin(IV) and, very likely, substitute partially Sn(4+) by Ga(3+). The reduction of Sn(4+) to Sn(2+) in the Cs(2)SnI(6) phase contributes to the switching from p-type conductivity to n-type, thereby improving the total concentration and mobility of negative-charge carriers. The phase composition of the samples obtained was studied by X-ray diffraction (XRD) and (119)Sn Mössbauer spectroscopy (MS). It is shown that the excess of metal gallium in a reaction melt leads to the two-phase product containing Cs(2)SnI(6) with Sn(4+) and β-CsSnI(3) with Sn(2+). UV–visible absorption spectroscopy shows a high absorption coefficient of the composite material.