Controlled Reduction of Sn in the Complex Iodide CsSnI 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 CsSnI by a reactive sintering method. The reducing power of gallium was applied to influence the optoelectronic properties of the CsSnI phase via partial reduction of tin(IV) and, very likely, substitute partially Sn by Ga. The reduction of Sn to Sn in the CsSnI phase contributes to the switching from -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 Sn Mössbauer spectroscopy (MS). It is shown that the excess of metal gallium in a reaction melt leads to the two-phase product containing CsSnI with Sn and β-CsSnI with Sn. UV-visible absorption spectroscopy shows a high absorption coefficient of the composite material.