Potassium chloride templated α-FAPbI3 perovskite crystal growth for efficient planar perovskite solar cells

For planar n-i-p device, SnO2/perovskite interface, which not only governs the electron extraction and transport, but affects perovskite formation, takes fundamental role to achieve perovskite solar cells (PCSs) with high performance in the context of commercializing courses. KCl treatment is one of the most effective and widely accepted strategy to optimize SnO2/perovskite interface. Whereas the role of KCl draws tremendous controversy, and needs further investigation. Thereby, we systematically investigated the influence of KCl treatment on optoelectronic properties of SnO2 and perovskite film, and the photovoltaic performance of PSCs. It is demonstrated that KCl treatment can suppress hydroxyl on SnO2 surface and improve charge extraction. In addition, KCl treatment can promote perovskite crystallization. Due to the well matched lattice constants of KCl and α-FAPbI3, we proposed that KCl may serve as seed crystal to guide FAPbI3 formation, while Cl further promotes perovskite crystal growth. Consequently, the solar cell based on SnO2/KCl exhibited promoted photovoltaic performance with efficiency increased from 19.51% to 20.65%, and improved thermal stability in ambient condition. Meanwhile, benefiting from the capability of promoting α-FAPbI3 crystallization of KCl treatment, MA-free device based on SnO2/KCl achieved increased efficiency from 19.03% to 20.42%.