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.