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.