Chemical bath deposited ZnS buffer layer for Cu(In,Ga)Se2 thin film solar cell

Abstract

The dependence of Zn precursors using zinc sulfate (ZnSO4), zinc acetate (Zn(CH3COO)2), and zinc chloride (ZnCl2) on the characteristics of the chemical bath deposited ZnS thin film used as a buffer layer of Cu(In,Ga)Se2 (CIGS) thin film solar cell was studied. It is found that the ZnS film deposition rate increases with higher stability constant during decomplexation reaction of zinc ligands, which affects the crack formation and the amount of sulfur and oxygen contents within the film. The band gap energies of all deposited films are in the range of 3.40–3.49eV, which is lower than that of the bulk ZnS film due to oxygen contents within the films. Among the CIGS solar cells having ZnS buffer layers prepared by different Zn precursors, the best cell efficiency with 9.4% was attained using Zn(CH3COO)2 precursor due to increased Voc mainly. This result suggests that [Zn(NH3)4]2+ complex formation should be well controlled to attain the high quality ZnS thin films.