Low-temperature interfacial engineering for flexible CsPbI2Br perovskite solar cells with high performance beyond 15%

Abstract

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.