Low-temperature interfacial engineering for flexible CsPbI2Br perovskite solar cells with high performance beyond 15%†
All-inorganic cesium lead halide (CsPbX3) perovskites exhibit superior thermal stability compared to their organic–inorganic hybrid counterparts. The power conversion efficiency (PCE) of CsPbI2Br perovskite solar cells (PSCs) has been over 16%. However, high-temperature annealing limits the feasibility of their application in flexible devices. Here, low-temperature processed flexible CsPbI2Br PSCs are designed by introducing Al-doped ZnO (AZO) as an electron-transport layer and tert-butyl cyanoacetate (t-BCA) as a passivation layer. The thickness-insensitive AZO significantly enhances the quality of the perovskite films and the reproducibility of the PSCs. t-BCA can effectively passivate the trap states and suppress charge recombination of CsPbI2Br films as well. The as-optimized flexible CsPbI2Br PSCs exhibit a high PCE of 15.08% (with an active area of 0.1 cm2), which is one of the highest efficiencies for flexible all-inorganic PSCs. The devices show outstanding stability, retaining 93% of their original PCE after being stored for 60 days, and retaining 91% and 86% of the initial efficiency after continuously heating for 360 hours at 85 °C and storing under 65% RH for 30 hours, respectively. In addition, the PSCs exhibit excellent mechanical stability, and retain 85% of their original value after 1000 bending cycles at a curvature radius of 3 mm.