This report describes the optimisation activity of the growth processes of Cu2FeSnS4 (CFTS) thin films (TFs) in order to validate this chalcogenide, which is made of naturally very abundant elements, as a new active material for solar cells, alternative to the most known Cu2ZnSnS4 (CZTS). RSE has already optimised the deposition of CZTS for photovoltaic (PV) applications; this was made using a two-step process, the sputtering deposition of the metal precursors and a subsequent oven treatment in the presence of sulphur vapours. Starting from the protocols already used for CZTS, in this activity a comparative study was conducted to assessing the versatility of the RSE process for also depositing chalcogenide TFs having different formulations. Through an appropriate selection of targets in sputtering sources, some series of CFTS samples were deposited to study how the main process parameters influence the chemical-physical characteristics of the TF, in a similar way to that which has already been made for CZTS. This approach promotes a better understanding of the suitability of the Cu-Fe-Sn-S element system for the deposition of TFs for PV applications, also highlighting the main differences with respect to the better known CZTS.
This work of deposition and characterisation of CFTS TFs was accompanied by an effort to update and deepen the specific literature on this material, which showed almost no activity aimed at the development of PV systems.
CFTS TFs were extensively characterised at a morphological, compositional and electrical level in order to: (i) study the reproducibility of the process; (ii) identify the best parameters to produce TFs with optimal characteristics for PV applications (e.g., purity, homogeneity and adhesion). Prototype PV cells were obtained from all the CFTS samples, using the same process already optimised for the CZTS, even though it was not possible to measure the PV performance for any of them. This behaviour is potentially attributable to low values of shunt resistance (induced by the presence of secondary conductive phases) and/or the high presence of defects both within the CFTS TFs and at the interface with the rear contact (in Mo) and/or with the CdS used for the p-n junction. Further experimental activities are essential to understand the real potential of CFTS for replacing CZTS.