Improved J_sc by Increasing the Absorber Layer Thickness of Monoclinic-Dominated Cu₂SnS₃ Thin Film Solar Cells Fabricated on Flexible Mo Foil

Cu2SnS3 (CTS) has various crystal structures and a wide bandgap energy range of 0.93-1.77 eV, depending on the crystal structure. The optical properties of CTS are very similar to those of Cu2ZnSnS4 (CZTS)-based materials, as reported extensively in the past and is therefore in the spotlight as an absorber material. However, CTS thin film solar cells (TFSCs) are mainly studied on non-flexible substrates, and little research has been focused on flexible substrates. When a flexible substrate is applied to CTS TFSCs, Zn is omitted from CZTS-based materials, reducing raw material costs and enabling a roll-to-roll fabrication process; hence, the economic benefit is doubled. When CTS TFSCs are fabricated on a Mo foil substrate, voids exist at the back interface and the device characteristics markedly deteriorate. To solve this problem, the thickness of the CTS absorber layer is increased in this study by doubling the thickness of the precursor. As a result, Cu, Sn, and S display a more uniform distribution in the absorber layer, which further improves the light-absorbing characteristics of CTS TFSCs. Finally, a device with a power conversion efficiency of 1.31% is obtained.