Path towards high-efficient kesterite solar cells

Kesterite structure semiconductor Cu2ZnSn(S,Se)4 is one of the most promising candidate as a light absorber material to overtake the next generation of thin film solar cells, owing to its low cost, non-toxic, and earth abundant source materials. The Shockley-Queisser limit of the single junction Cu2ZnSn(S,Se)4 solar cell is over 30%, signifying a large potential of this family of solar cells. In the past years, with the development of synthesis techniques, Cu2ZnSn(S,Se)4 solar cells have attracted considerable attention and the power conversion efficiency of Cu2ZnSn(S,Se)4 solar cell has experienced a rapid progress. Presently, the certified champion efficiency of CZTSSe solar cells has reached to 12.6%, which is far below the efficiency of Cu(In,Ga)Se2 solar cell. In this review, the developments of Cu2ZnSn(S,Se)4 solar cells in recent years are briefly reviewed. Then the fundamental understanding of Cu2ZnSn(S,Se)4 solar cells is introduced, including materials and device structure, as well as the band alignment of hetero-junction and their impacts on device performance. After that, we mainly review the progress and achievements in the preparation processes, through vacuum and non-vacuum based processes. Finally, we outline the challenges and perspectives of this promising solar cell.