Dewei Zhao1 Yue Yu1 Changlei Wang1 Chong Chen1 Zhaoning Song1 Kai Zhu2 Yanfa Yan1

1, University of Toledo, Toledo, Ohio, United States
2, National Renewable Energy Laboratory, Golden, Colorado, United States

Because of the low-temperature process and high device efficiency, organic-inorganic metal halide perovskite absorbers offer an unusual opportunity for fabricating low-cost, high efficiency polycrystalline perovskite thin-film tandem solar cells. Tandem solar cells combining wide-bandgap and low-bandgap subcells can be fabricated in the two-terminal (2-T) or four-terminal (4-T) configuration, each exhibiting unique advantages. In this talk, we will present our recent results on the optimization of the subcells and the resulting 4-T and 2-T tandem cells. For the wide-bandgap subcell, we use FA0.8Cs0.2Pb(I0.7Br0.3)3 as the absorber, which exhibits a bandgap of ~1.75 eV. For the low-bandgap subcell, we use FA0.6MA0.4Sn0.6Pb0.4I3 as the absorber, which has a bandgap of ~1.25 eV. We further applied various approaches such as using additives and/or post-deposition treatment to improve the quality of the absorbers. We will also discuss key challenges experienced in fabricating high efficiency tandem solar cells.