¹¹⁹Sn MAS NMR to Assess the Cationic Disorder and the Anionic Distribution in Sulfoselenide Cu₂ZnSn(S_<i>x</i>Se_1–<i>x</i>)₄ Compounds Prepared from Colloidal and Ceramic Routes

Abstract

Crystalline powders of the photovoltaic material candidate copper zinc tin sulfoselenide Cu2ZnSn(SxSe1–x)4 (CZTSSe) with x = S/(S + Se) from 0 to 1 were characterized by 119Sn solid state nuclear magnetic resonance (NMR) and by powder X-ray diffraction (PXRD). Two series of powders were characterized: one synthesized by a ceramic route and having cationic stoichiometry 2:1:1 and another one synthesized by a colloidal route, having a cationic Cu-poor Zn-rich composition and used as precursors for photovoltaic active films. The homogeneous anionic composition of the samples, which is a feature needed for the NMR analysis of the anionic distribution, has been proved by PXRD. The x values determined from the quantitative analysis of the 119Sn spectra are in very good agreement with those deduced by PXRD. In addition, the 119Sn spectra reveal, for the first time, the random distribution of the chalcogen atoms, which seems to be a general process. Finally, a qualitative, but thorough, analysis of the line width of the 119Sn NMR spectra was undertaken to investigate the Cu/Zn cationic disorder, a feature which can seriously affect the optoelectronic properties of CZTSSe. The cationic disorder turns out to be dependent on the type of cationic composition. Indeed, regardless of x ratios and the synthesis methods, our samples containing A-type defect complexes [VCu + ZnCu] are less prone to Cu/Zn disorder.