Mapping and comparison of the shortcomings of kesterite absorber layers, and how they could affect industrial scalability

Kesterite absorber layers for thin film solar cells are promising in terms of cost and material abundance, but still lag relatively far behind Cu(In,Ga)(S,Se)2 in terms of device efficiency. This raises questions about their potential for large-scale production. This work aims at assessing the challenges of scaling up the existing Physical Vapor Deposition processes of Cu2ZnSnSe4, Cu2ZnSnS4 or Cu2ZnSn(S,Se)4 for industrial fabrication. The main issues that can affect kesterite and their causes are listed and prioritized in terms of criticality for the performance, using the methodology of Design Failure Mode and Effects Analysis. This analysis indicates, in particular, that bandgap and potential fluctuations are, to date, the most critical risk factors for the absorber, because of the inability to prevent them in the current state of our understanding. Applying the acquired knowledge to the known fabrication routes for kesterite, we analyze how some of these shortcomings can originate from unsuitable metallic ratios in the precursor and the absorber due in particular to the Sn loss in kesterite fabrication processes. In the most efficient devices to date, this loss forces the sequential route (i.e. deposition/selenization) on what are historically 1-stage processes (co-evaporation, reactive sputtering) developed for industrial Cu(In,Ga)(S,Se)2 fabrication.