Double Side Interfacial Optimization for Low-Temperature Stable CsPbI₂Br Perovskite Solar Cells with High Efficiency Beyond 16%

CsPbI₂Br perovskite solar cells have achieved rapid development owing to their exceptional optoelectronic properties and relatively outstanding stability. However, open-circuit voltage (V_oc) loss caused by band mismatch and charge recombination between perovskite and charge transporting layer is one of the crucial obstacles to further improve the device performance. Here, we proposed a bilayer electron transport layer ZnO(bottom)/SnO₂(top) to reduce the V_oc loss (E_loss) and promote device V_oc by ZnO insert layer thickness modulation, which could improve the efficiency of charge carrier extraction/transfer and suppress the charge carrier recombination. In addition, guanidinium iodide top surface treatment is used to further reduce the trap density, stabilize the perovskite film and align the energy levels, which promotes the fill factor, short-circuit current density (J_sc), and stability of the device. As a result, the champion cell of double-side optimized CsPbI₂Br perovskite solar cells exhibits an extraordinary efficiency of 16.25% with the best V_oc as high as 1.27 V and excellent thermal and storage stability.