Guanidinium doping enabled low-temperature fabrication of high-efficiency all-inorganic CsPbI2Br perovskite solar cells

All-inorganic perovskite CsPbI2Br usually requires a high fabrication temperature (higher than 200 °C) and suffers from an unwanted phase transition from a photo-active cubic phase to a photo-inactive orthorhombic phase. Here, we demonstrate an effective anti-solvent-free route to simultaneously stabilize the cubic phase and lower the fabrication temperature of perovskite solar cells with guanidinium (GA) cation doping. It is suggested that a trace amount of GA in the precursor could enter the substitutional sites to stabilize the cubic phase by relaxing the lattice strain and forming strong hydrogen bonds. State-of-the-art in situ grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements reveal that GA could advance the crystallization of the cubic phase, indicating that the formation of the perovskite cubic phase experiences a lowered energy barrier with the assistance of GA, thereby resulting in a significant decrease of the fabrication temperature. An efficiency as high as 14.34% was achieved at a low fabrication temperature of 140 °C. With the help of GA, the device maintains ∼94% of its initial efficiency after being stored for 1000 h.