Interface Engineering for All-Inorganic CsPbI₂ Br Perovskite Solar Cells with Efficiency over 14

In this work, a SnO₂ /ZnO bilayered electron transporting layer (ETL) aimed to achieve low energy loss and large open-circuit voltage (V_oc ) for high-efficiency all-inorganic CsPbI₂ Br perovskite solar cells (PVSCs) is introduced. The high-quality CsPbI₂ Br film with regular crystal grains and full coverage can be realized on the SnO₂ /ZnO surface. The higher-lying conduction band minimum of ZnO facilitates desirable cascade energy level alignment between the perovskite and SnO₂ /ZnO bilayered ETL with superior electron extraction capability, resulting in a suppressed interfacial trap-assisted recombination with lower charge recombination rate and greater charge extraction efficiency. The as-optimized all-inorganic PVSC delivers a high V_oc of 1.23 V and power conversion efficiency (PCE) of 14.6%, which is one of the best efficiencies reported for the Cs-based all-inorganic PVSCs to date. More importantly, decent thermal stability with only 20% PCE loss is demonstrated for the SnO₂ /ZnO-based CsPbI₂ Br PVSCs after being heated at 85 °C for 300 h. These findings provide important interface design insights that will be crucial to further improve the efficiency of all-inorganic PVSCs in the future.