Simplified interconnection structure based on C60/SnO2-x for all-perovskite tandem solar cells

The efficiencies of all-perovskite tandem devices are improving quickly. However, their complex interconnection layer (ICL) structures—with typically four or more layers deposited by different processes—limit their prospects for applications. Here, we report an ICL in all-perovskite tandem cells consisting merely of a fullerene layer and a SnO2–x (0 < x < 1) layer. The C60 layer is unintentionally n-doped by iodine ions from the perovskite and thus acts as an effective electron collecting layer. The SnO2–x layer, formed by the incomplete oxidization of tin (x = 1.76), has ambipolar carrier transport property enabled by the presence of a large density of Sn2+. The C60/SnO1.76 ICL forms Ohmic contacts with both wide and narrow bandgap perovskite subcells with low contact resistivity. The ICL boosts the efficiencies of small-area tandem cells (5.9 mm2) and large-area tandem cells (1.15 cm2) to 24.4% and 22.2%, respectively. The tandem cells remain 94% of its initial efficiency after continues 1-sun illumination for 1,000 h. Interconnecting layers are critical to the efficiency of tandem solar cells and a high number of layers is typically needed to ensure good electrical properties. Yu et. al show that a fullerene/tin-oxide interconnecting layer enables 24.4% efficiency and improved stability in all-perovskite tandem solar cells.