Experimental and theoretical advances in Cu₂ZnSn(S,Se)₄ solar cells

Cu₂ZnSn(SSe)₄ (CZTSSe) semiconductor is quite promising to solar cell applications, recently achieving a new record efficiency of 14.9%. Despite theoretical works have shown that efficiencies higher than 20% are possible in this technology, there are some critical points that should be carefully solved by the scientific community. In this review, it is presented a critical analysis on the state-of-the-art of Cu₂ZnSn(SSe)₄ solar cells. First, we summarize advantages and disadvantages of most used vacuum and non-vacuum thin film fabrication methods, followed by the most important results in solar cell fabrication along with key factors in performance improvement. Furthermore, the future experimental outlook is also analyzed with a particular focus on kesterite material engineering and its grading band-gap engineering. Likewise, the experimental state-of-the-art of CZTSSe device fabrication, a non-typical contribution of this work to the literature it is the presentation and discussion of most important theoretical results on solar cells. A particular attention is paid to results concerning numerical and analytical approaches for the study of Cu₂ZnSn(SSe)₄ solar cells. Finally, theoretical results concerning the potential use of nanostructured CZTSSe solar cells for achieving efficiencies higher than that of the Shockley-Queisser limit are presented and discussed.