Growth behavior of co-electrodeposited CZTS precursor thin films from acidic baths containing tartaric acid

We synthesized Cu₂ZnSnS₄ precursor thin films on Molybdenum-coated soda lime glass substrates using a single-step co-electrodeposition process. The as-deposited films, however, were severely Zn-poor, Sn-rich and S-poor, possessing rough, powdery surface morphologies. In this study, the effects of deposition potential, deposition time, and bath composition on the stoichiometries and morphologies of the as-deposited films are systematically investigated, with the aims to understand the growth behavior and to improve the film properties. The poor morphologies of the initial films are attributed to diffusion-limited growth modes and hydrogen co-evolution. Removal of the tartaric acid from the bath increases the bath pH, decreases the hydrogen evolution reaction, and significantly improves the film compositions and morphologies. Possible mechanisms to describe the observed deposition behavior, morphology trends, and composition trends are discussed.