Alkali metal fluoride etching for efficient and stable planar TiO2 perovskite solar cells

Abstract

Recently, significant advancements have been made in organic–inorganic hybrid perovskite solar cells. Nonetheless, durability poses a major challenge for their commercial viability. The interface within the perovskite absorber layer is pivotal to the photoelectric properties and stability of these devices. In n–i–p devices, defects often arise on the electron transport layer surface (such as titanium oxide) because of their lower formation energy. This research explored the effect of different alkali metal cations on device performance through chemical treatment of the titanium oxide surface using a blend of alkali metal fluoride salts and diluted HCl. The results showed that KF treatment effectively passivated defects among all fluoride salts, leading to improved device performance. The device processed with KF achieved a peak PCE of 25.15%, accompanied by superior storage and operational stability. Devices treated with KF maintained over 88% of their initial efficiency following 1000 hours of uninterrupted exposure to illumination under MPPT conditions, outperforming control devices.