All-inorganic perovskites, such as CsPbI2Br, have attracted increasing attention because of its potentially better thermal stability. However, a high-quality CsPbI2Br perovskite film usually requires a high fabrication temperature (> 200 ºC) and suffers from unwanted phase transition from a photo-active cubic phase to a photo-inactive orthorhombic phase.
In this work, we present a brand-new means to simultaneously stabilize the photo-active cubic phase and lower the fabrication temperature of perovskite solar cells with guanidinium cations (GA) doping. The crystallization process of CsPbI2Br is investigated by state-of-art in situ grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements to understand the crystallization process and guide the device fabrication. It is revealed that GA could advance the crystallization of the cubic phase as well as suppress the unwanted phase transition to the orthorhombic phase, indicating the formation of perovskite cubic phase experiences a lowered energy barrier with the assistance of GA. The film is further treated with the GABr to passivate the surface trap states by inducing a secondary crystal growth, which could give rise to enhanced crystallinity and orientational order. An efficiency as high as 14.34% was achieved with an industrial-friendly low-temperature and antisolvent-free fabrication process. The device could maintain ~94% of its initial efficiency after being stored for 1000 h. This work not only provide a facile way to improve the structural stability and efficiency of all-inorganic PSCs, but also uncover the underlying crystallization mechanism of large organic cations in promoting crystallization process of the perovskite α-phase.
Manuscript by Ma and Qin et al. was just accepted by Journal of Materials Chemistry A, 2019, DOI:10.103/c9ta108899h.