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

摘要

Cu2ZnSnS4 (CZTS) thin films were synthesized by the sol-gel method using two kinds of mixture solvents with post annealing at 550 °C. Solutions were prepared by dissolving copper (II) chloride dihydrate (CuCl2 · 2H2O), zinc (H) 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) Ω · 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.