Simplified interconnection structure based on C₆₀/SnO_2-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 SnO_2–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 SnO_2–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/SnO_1.76 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.