Investigation of the electrochemical growth of a Cu-Zn-Sn film on a molybdenum substrate using a citrate solution

Cu–Zn–Sn (CZT) metallic films were electrodeposited on molybdenum-coated soda lime glass (Mo/SLG) substrates at a constant potential using an aqueous electrolyte solution containing Cu (II), Zn (II), Sn (II) ions, and tri-sodium citrate. The electrochemical growth process of the CZT film has been elucidated by analysis of the film thickness, charge consumption, elemental and phase composition, and surface morphology. Interestingly, it was found that only copper and tin were deposited in the initial stage (30 s) of electrodeposition, and after this zinc began to be incorporated into the film. Further study revealed that H2 evolution was responsible for the failed deposition of zinc on the Mo substrate. The grain size of the CZT film increased over the deposition time. It was also found that the film thickness (except for the first 1 min) increased linearly with the charge consumption, and the film grew at a constant rate. As a result, the composition of the CZT film remained constant throughout the deposition process and copper, tin, and zinc were distributed evenly in the film. Alloy phases of Cu6Sn5 and Cu5Zn8 were found in the CZT film and they were largely constant during the growth of the film. The new insight into the electrodeposition process of CZT films will be very useful for the production of high-quality solar active materials such as Cu2ZnSnS4 and Cu2ZnSnSe4