Flexible Monolithic 2-terminal Kesterite Cu2ZnSnSe4 /Perovskite Tandem Solar Cells

Abstract Currently, perovskite/Si tandem record cell exceeded 33% efficiency which is higher than a theoretical Si single-junction cell. Given poor flexible Si cells and high demands on BIPV, fabrication of high-efficiency flexible solar cells is essential. Earth-abundant kesterite photovoltaics attract strong attention due to high flexibility and low fabrication cost. Nevertheless, challenges to realize high-efficiency flexible kesterite solar cells remain because of high-growth temperature and rough surface. In this work, the Ag incorporation in CZTSe film addresses aforementioned material and process issues. The highest efficiency of 7.3% has been achieved among flexible CZTSe single-junction cells on polyimide substrate. Moreover, we successfully demonstrated a CZTSe/perovskite tandem solar cell with 16.4% (on glass) and 11.35% (on flexible PI). These results imply that Ag incorporation is a universal method to offer a promising approach to produce flexible chalcogenide solar cells and tandem device applications.