Impact of capping during the formation of Cu2ZnSn(S,Se)4 thin films

Major challenge for the fabrication of kesterite absorber thin films such as CZTSSe (Cu2ZnSn(S,Se)4) is the volatility of chalcogens. Material loss and poor morphology are two key issues during high temperature annealing, carried out for the formation of CZTSSe thin film absorber layers. The purpose of the present study is to investigate the influence of capping during the crystallization of precursor to CZTSSe films via annealing. In this work, initial precursor was synthesized from elemental constituents by ball milling. CZTSSe films were deposited by doctor's blade process. Annealing was carried out in two different atmosphere viz. vacuum and inert gas. Both sets of samples were annealed with and without capping. We found significant changes for different annealing atmospheres. Capping has a positive influence on the film properties, revealed by structural, morphological and compositional analysis. Capping reduced material loss of volatile constituents and resulted compact crystalline films.