Manganese-substituted Kesterite thin films for Earth-abundant photovoltaic applications

Thin film low-cost and eco-friendly photovoltaic devices are based on Cu2ZnSn(S,Se)4. To reduce production costs and improve sustainability, manganese can substitute zinc since Mn is safe and Earth-abundant, and it can be used as a light absorber1) Here, we report on the growth and characterization of Cu2MnSnS4 thin films, produced both by a two-step deposition process and by a sol-gel-based method. The metallic precursors have been deposited by sputtering, and the stack annealed at high temperatures in sulphur atmosphere. The layers, obtained in a Cu-poor and Mn-poor compositional regime, have been tested in solar devices with a record efficiency of 1.13%, with an open-circuit voltage of about 445 mV, delivered after over one year from the first PV measurement. X-ray diffraction and photoelectron, Raman, photoluminescence, and admittance spectroscopies have been used to characterize Cu2MnSnS4, and a scenario of high defectivity has emerged.2) Therefore, we moved to a sol-gel-based method, to improve the quality of the material reducing defectivity. An ink, prepared by dissolving in dimethyl-sulfoxide metal salts and thiourea, used as the only source of sulphur, was deposited by blade coating to obtain thin films. Sol-gel transition took place in air and then samples were annealed at 550°C under argon atmosphere. The so obtained thin films were fully characterized showing promising preliminary results. 1)Le Donne A. et al., Front. Chem, 2019, 7:297. 2)Trifiletti V. et al., Solar Energy Materials & Solar Cells, 2023, 254 112247.