Existence of off stoichiometric single phase kesterite

In this work the flexibility of the kesterite structure is discussed. It is shown that kesterite type CZTS and CZTSe can deviate from stoichiometric composition by the formation of intrinsic point defects leading to different off stoichiometric kesterite types. For this study off stoichiometric CZTS and CZTSe powder samples have been synthesized by solid state reaction from pure elements. Their chemical composition was determined by WDX spectroscopy and the structural characterization was conducted by X ray diffraction. Amongst the studied 49 samples, a number of them have been identified to contain only an off stoichiometric kesterite type phase which exhibit Cu poor Zn rich composition. On the other hand, Cu rich Zn poor kesterite type CZTS and CZTSe always coexists with secondary phases. Thus it has been demonstrated, that the kesterite type structure can self adapt to Cu poor and Cu rich compositions in CZTS and CZTSe without any structural change except the cation distributio