Simplified interconnection structure based on C60/SnO2-xfor 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 C(60)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 C-60/SnO1.76ICL 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 mm(2)) and large-area tandem cells (1.15 cm(2)) 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.