Postpassivation of Multication Perovskite with Rubidium Butyrate
José Carlos Germino, Rodrigo Szostak, Silvia G. Motti, Raphael F. Moral, Paulo E. Marchezi, Heitor Secco Seleghini, Luiz G. Bonato, Francineide Lopes de Araújo, Teresa Dib Zambón Atvars, Laura M. Herz, David P. Fenning, Anders Hagfeldt, Ana F. Nogueira
Abstract
Many multication perovskites for highly stable and efficient solar cells benefit from rubidium iodide introduced in the precursor solution. It is well-known that Rb+ influences positively the optoelectronic and mobility properties and has a direct effect upon crystallization and halide homogenization. As Rb+ is often incorporated by adding RbI in the precursor solution, it can be difficult to distinguish the influence of Rb+ and I– separately. Herein, we report a postpassivation of methylammonium-free (CsFA) perovskite films with rubidium butyrate (RbBu). The passivation with RbBu increases the hydrophobicity of the perovskite surface and passivates shallow and deep traps, leading to an increase of charge-carrier lifetimes and diffusion lengths. Consequently, a better photovoltaic performance is also observed. These superior properties are attributed to both surface (halide-vacancy) and grain-boundary passivation by the carboxylate group and Rb+, respectively. We found that Rb+ itself acts as a direct and powerful passivating agent for multication perovskites, and this is proven by decoupling its contribution and halide’s contribution to other important performance parameters (e.g., crystallization, halide vacancies filling, etc.).