Controlled crystallinity and morphologies of 2D Ruddlesden-Popper perovskite films grown without anti-solvent for solar cells

Two-dimensional (2D) Ruddlesden-Popper (RP) perovskite films have attracted considerable attention for the environmentally stable perovskite solar cells. However, there is a big space for improving the film crystallinity and its crystallographic orientation to enhance the efficiency of solar cells. In addition, the assistance of anti-solvent is commonly used to obtain a better crystallinity and orientation of 2D RP perovskite films. Nevertheless, the anti-solvent method produces a lot of volatile organic compounds toxic to human health and is challenging to control. Here, we prepared 2D RP perovskite (PEA)2(MA)4Pb5I16 (n = 5) films with the assistance of methylammonium chloride (MACl) additive via a simple one-step deposition method by avoiding anti-solvent treatment. The MACl additive is believed to induce the formation of an intermediate phase composed of perovskite crystals without annealing, which directly promotes the vertical alignment of 2D RP perovskite films on the substrate. The 2D RP films deposited on the mesoporous TiO2 electron transport layer showed high crystallinity and preferential vertical crystallographic orientation. The resulting devices exhibited a power conversion efficiency of 9.7%, much higher than that of the devices prepared without MACl (0.66%).