We have investigated synthesis conditions and different properties of the quaternary Cu2ZnSn(SexS1 - x)(4) (x = 0.3) (CZTSSe) monograin powders in order to determine the best preparation conditions for the realization of CZTSSe powder as absorbermaterial in monograin layer solar cells. CZTSSe powders with different initial compositions were synthesized in the liquid phase of potassium iodide flux in evacuated quartz ampoules. Energy dispersive X-ray spectroscopy studies revealed that Cu/(Zn+ Sn) ratio of final powder can be changed from 0.91 to 1 and ZnSn ratio from 0.9 to 1.04. Raman spectra of the CZTSSe monograin powders showed peaks of some secondary (mostly binary) phases. To improve the properties of synthesized powders as-grown monograins were heat-treated in sealed quartz ampoules in controlled Se, S and SnS2 atmospheres using a two-temperature zone arrangement. It was found that the effect of heat-treatments on the output parameters of CZTSSe monograin layer solar cells depends strongly on the initial powder composition. (C) 2012 Elsevier B.V. All rights reserved.