This report describes the activities undertaken to optimize the growth and finalization processes of photovoltaic (PV) solar cells based on Cu₂ ZnSnS₄ (CZTS) thin films (TF). In order to better plan and direct the experimental activity, an in-depth analysis of the reference literature was carried out. Particular attention was paid to identifying a number of innovative processes described in the literature to maximize the performance of these PV devices. At RSE, the CZTS was deposited using a two-step process, which involves the deposition of metal precursors by sputtering, followed by sulphurization. With regard to the other layers used to finalize these PV devices, particular attention has been paid both to optimizing the molybdenum (Mo) thin film (TF) used as a contact on the back of the device, and to the effect of process parameters on the deposition of cadmium sulphide (CdS), which, coupled to the CZTS, forms the p-n junction of the device.

By optimizing the main process parameters, both at the CZTS deposition level and at the PV cell finalization level, samples with an efficiency of ≈3% were obtained, while at the same time the good reproducibility of the process, even for large samples (3.5 x 7.5cm²), was verified. To further improve performance, the effects of introducing two innovative treatments during the finalization phase of the device were studied: i) a post-sulfuration chemical treatment and ii) a post-CdS deposition thermal treatment. The combination of these processes led to an improvement in the final performance of over 35%. The best CZTS-based cell produced at RSE during this activity obtained a conversion efficiency of about 4.5%, with Jsc=15.1mA cm^-2, Voc 561mV and FF=54%.

Overall, the results obtained, both in terms of performance and system control, indicate a good reproducibility of the production process adopted and are therefore essential starting points for the next activities in which the validation of new high natural abundance chalcogenides (CFTS and CMTS) for PV applications is foreseen.