Tailoring CZTSSe Solar Cell Performance: Comparison of Flexible Molybdenum Foil and Sputtered Molybdenum Back Contacts

Flexible CZTSSe (Cu₂ZnSn(S,Se)₄) solar cells on flexible molybdenum foil (MF) substrates are showing promise for being a candidate for the next-generation large-area and lightweight solar technologies. However, the nature of the back contact continues to be a decisive factor influencing absorber morphology, crystallinity, and the ultimate final device performance. In this work, we provide a comprehensive analysis and comparison of a variety of back contact configurations of flexible and rigid Mo substrates. We analyze four configurations in detail: MF, sputtered Mocoated MF, 10 nm NaF-coated MF, and MoOx-interlayered MF. We compare these with standard rigid devices on sputtered Mo on soda-lime glass (SLG) substrates.The work examines the impact of each back contact on the CZTSSe absorber growth behavior based on grain size, grain distribution, and defect passivation. Furthermore, solar devices are also prepared and examined to find the impact of back contact engineering on the main performance characteristics.