Secondary phases dependence on composition ratio in sprayed Cu2ZnSnS4 thin films and its impact on the high power conversion efficiency

In this work we report the relation between different secondary phases formation and the values of Cu/(Zn+Sn) and Zn/Sn ratios of Cu2ZnSnS4 (CZTS) thin films deposited by pneumatic spray pyrolysis using air as carrier gas. The films were grown on soda lime glass substrates via (CH3COO)2·Zn·2H2O, CuCl2·2H2O, SnCl2·2H2O and thiourea as precursors salts in the solution. The secondary phases present in the films were determined from Raman spectroscopy and the chemical composition of the elements from X-ray fluorescence (XRF) measurements. Varying the growth parameters and post-deposition thermal and chemical KCN treatments we have studied the different secondary phases formation dependence on the values of the Cu/(Zn+Sn) and Zn/Sn ratios and its impact on the properties of polycrystalline thin films solar cells where CZTS is used as the absorber layer.