Combined-solvent engineering of HPbI3 for efficient FAPbI3 perovskite solar cells

Abstract

Hybrid organic−inorganic halide perovskite solar cells have experienced a rocket-rising in efficiency, reaching a certified value beyond 25%. Tremendous jobs have been done on the CH3NH3PbI3 system to improve the efficiency. However, there are less studies have been done on the FAPbI3 system. And it is still difficult to form a pure α phase FAPbI3 with high surface coverage and big grain size at the same time. In this work, a combined-solvent engineering is proposed to deposit HPbI3 film with a roughness of only 5 nm. We obtained the uniform HPbI3 film by anti-solvent dripping during the spin of the DMF/NMP mixed solvent with equal molar ratio of PbI2 and hydrogen acid. Finally, it allows formation of high surface coverage, large grain size and pure α phase FAPbI3 perovskite films by the two-step method. A champion PCE of 18.2% as well as an average efficiency of 17.4% is finally achieved in the inverted planar cells with a high current density of 24.3 mA cm-2. The results illustrate this method is a convenient route for the deposition of pure FAPbI3 films, demonstrating great potential for higher efficiency of single junction device and further commercialization.