Investigation of Cu₂ZnSnSe₄ thin films by atomic force microscopy

In comparison to the traditional use of glass substrates, the thin films onto metal substrates offer improved device cooling, economical large-scale roll-to-roll processing, and applicability in lightweight, as well as flexible products. However, unlike glass, metal foils tend to exhibit rough surfaces. This article studies the substrate-type (Mo/glass and Mo-foil) effect on the topographic characteristics of the Cu₂ZnSnSe₄ films by atomic force microscopy (AFM). Cu₂ZnSnSe₄ thin films were prepared by the electrodeposition of stack copper/tin/copper/zinc (Cu/Sn/Cu/Zn) precursors, followed by selenization. AFM was used to study the topographic characteristics of thin films, including grain size, surface roughness, and maximum height of the profile. It is shown that the films obtained on Mo/glass and Mo-foil substrates have similar roughness and in the both cases the grain structure is formed. The Cu₂ZnSnSe₄ thin films show relatively high surface roughness and maximum roughness profile height compared to Cu-Zn-Sn precursors. The increase in the surface roughness of the films was caused by the growth of grains during annealing and selenization processes. (authors)