Comparison of Flexible Molybdenum Foil and Sputtered Molybdenum Back Contacts for CZTSSe Solar Cells

Molybdenum foil (MoF) flexible substrates have attracted significant interest in fabricating kesterite thin-film solar cells, thanks to their potential for lightweight, flexible, and large-scale applications. However, one of the main key challenges with MoF is the absence of sodium, typically introduced from soda-lime glass (SLG) substrates, which is critical in enhancing CZTSSe film quality. To address this, a thin layer of NaF has been deposited on top of the MoF to balance the absence of sodium and thus enable enhanced grain growth and crystallinity. In this paper, the deposition processes were optimized systematically with respect to absorber quality and device performance. Solar cells have been characterized, and their performance has been compared with reference devices processed on sputtered Mo. Preliminary results showed low-performing devices based only on Mo foil. However, upon incorporating the pre-deposited NaF layer, efficiency increased to 2.5%. These preliminary results suggest that Mo foil is a promising substrate for flexible CZTSSe solar cells and, upon optimization, could reach performance comparable to standard devices on sputtered Mo back contacts.