Impact of Cu2ZnSn(SexS1 − x)4 (x = 0.3) compositional ratios on the monograin powder properties and solar cells

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 absorber material 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 Zn/Sn 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.

► The final composition of monograin powders is changeable in quite small region. ► Varying the initial metal ratios changes the S/Se ratio in the final powders. ► S and SnS2 vapor-treatments improve the parameters of monograin layer solar cells. ► Thermal treatments changed the S/(S + Se) ratio of the monograins. ► Best solar cell characteristics were achieved with Cu/(Zn + Sn) ratio of 0.88–0.92.