Abstract:Thin film solar cells have reached commercial maturity and extraordinarily high efficiency that make them competitive even with the cheaper Chinese crystalline silicon modules. However, some issues (connected with presence of toxic and/or rare elements) are still limiting their market diffusion. For this reason new thin film materials, such as Cu 2 ZnSnS 4 or SnS, have been introduced so that expensive In and Te, and toxic elements Se and Cd, are substituted, respectively, in CuInGaSe 2 and CdTe. To overcome the abundance limitation of Te and In, in recent times new thin film materials, such as Cu 2 ZnSnS 4 or SnS, have been investigated. In this paper we analyze the limitations of SnS deposition in terms of reproducibility and reliability. SnS deposited by thermal evaporation is analyzed by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and atomic force microscopy. The raw material is also analyzed and a different composition is observed according to the different number of evaporation (runs). The sulfur loss represents one of the major challenges of SnS solar cell technology.

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The state of the art of the second-generation of solar cells based on the CdTe and CuInGaSe 2 thin film technology will be described. This type of cells reached, on laboratory scale, photovoltaic conversion efficiencies respectively of 16.5% and 20.3% very close to those obtained with bulk materials. In particular, the materials, the layer sequences and deposition techniques used for the preparation of these two absorbers are described. Particular emphasis will be placed on major innovations that have enabled us to achieve high efficiencies with polycrystalline materials, showing how thin-film technology is mature enough to be transferred to industrial production. Finally, we will discuss about a project of technology-transfer developed at Parma University for the production of photovoltaic modules at an industrial level. In the near future, with our process, Arendi S.p.A. will reach a productivity of 18 MW/year.

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