Properties of kesterite Cu2ZnSnS4 (CZTS) thin films prepared by sol-gel method using two types of solution

Abstract

Cu2ZnSnS4 (CZTS) thin films were synthesized by the sol-gel method using two kinds of mixture solvents with post annealing at 550 degrees C. Solutions were prepared by dissolving copper (II) chloride dihydrate (CuCl2 center dot 2H(2)O), zinc (II) chloride (ZnCl2), tin (II) chloride (SnCl2) and thiourea (SC (NH2)(2)) into mixed solvents of 2-methoxy-ethanol and mono-ethanolamine (2-metho/MEA) and methanol and de-ionized water (methanol/DIW). CZTS films attained from both solutions are oriented to the (112) plane, indicating kesterite structure. Compared to methanol/DIW solvent, reduced void defects and better surface roughness are observed using 2-metho/MEA solvent, attributable to different vaporization tendency of constituents in the solutions. Raman and energy dispersive spectroscopy indicates that secondary phases such as Cu2SnS3 and SnS2 are present as a result of Zn-poor and Sn-rich components in the film, but 2-metho/MEA solvent produces less secondary phases and compositional ratio is closer to ideal value. Optical energy band gap and resistivity of CZTS thin film with 2-metho/MEA solvent are 1.27 eV and 2.7 x 10(-1) Omega . cm, respectively, which are suitable for an absorber layer in thin film solar cell. These results suggest that material properties of the sol-gel processed CZTS thin film are strongly affected by types of solvent in the solution.