This report describes the activities carried out by RSE to validate two new chalcogenides, Cu2MnSnS4 (CMTS) and Cu2FeSnS4 (CFTS), as alternatives to the better known Cu2ZnSnS4 (CZTS) as active element-based materials with high natural abundance for thin-film photovoltaic (PV) cells (FS). With regard to CMTS, detailed characterizations were carried out in this line of work (LA1.08), both at the device level (Admittance Spectroscopy (AS)) and of the active material alone (XPS analysis, X-ray Photoelectron Spectroscopy), in order to understand the origin of the discrepancy between the apparent good quality of the FS, deposited in a two-step process at RSE, and the reduced performance of the corresponding PV cells. A new set of CMTS samples was also deposited to study the interdependence between chemical composition, the presence of compositional gradients (particularly for Sn) and secondary phase formations.

AS measurements on both the CMTS samples from the previous three-year RdS and these new samples showed the presence of different defect types between CZTS and CMTS, but confirmed that post-deposition treatments (PDT) optimized to improve the performance of CZTS-based cells are also beneficial for CMTS-based devices. However, the presence of oxygen, detected in the FS by XPS analysis, seems to be the main issue behind the very low PV performance detected for all CMTS samples deposited so far, and this may be the basis for future research on this chalcogenide. Regarding CFTS, having set aside the possibility of using the two-step process for the deposition of this chalcogenide investigated in the previous three-year RdS, the synthesis of mono-crystalline (monograin) grains was carried out to be used for the development of PV cells at FS based on “monograin-layer (MGL)” technology. From literature findings, this technique has already shown promise for the development of PV devices based on other chalcogenides.

The synthesis of CFTS monograins was investigated and optimized to obtain powdered samples with grains with reduced particle size dispersion, similar particle geometry, and high crystallographic purity. This activity was conducted in collaboration with UNIMIB and Tallinn University, and results obtained confirm the opportunity to continue on this research path. Exploring new application areas, CFTS was also preliminarily tested as an anode material for sodium ion batteries.