Metal chloride precursor synthesization of Cu2ZnSnS4 solar cell materials

Cu2ZnSnS4 (CZTS) thin films with kesterite structures were prepared by directly sol-gel synthesizing spin-coated precursors on soda-lime-glass (SLG) substrates. The CZTS precursors were prepared by using solutions of copper (II) chloride, zinc (II) chloride, tin (IV) chloride, and thiourea. The ratio of SnCl4 in the precursors was found to play a critical role in the synthesization of CZTS. CZTS phases of SnS and SnS2 were observed in the synthesized films as prepared using precursors with a close to stoichiometric ratio of CuCl2:ZnCl2:SnCl4:CH4N2S = 4:1:1:8, where SnCl4 was 1 mol/l. The amounts of the educed SnS and SnS2 phases observed in the SEM images could be readily reduced by decreasing the volume of SnCl4 in the mixed solution. With decreasing amount of SnCl4 from 1 mol/l, the as prepared CZTS reveals a significant improvement in its crystalline properties. In this work, CZTS with an average absorption coefficient and an optical energy gap of over 104 cm−1 and ~1.5 eV, respectively, was obtained using precursors of copper (II) chloride, zinc (II) chloride, tin (IV) chloride, and thiourea mixed in a ratio of 2:1:0.25:8, and it had good crystallinity revealing a Cu-poor composition.