Postpassivation of Multication Perovskite with Rubidium Butyrate

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 Iseparately.Herein, we report a post-passivation 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 chargecarrier 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 contribuition and halide's contribuition to other important performance parameters (e.g. crystallization, halide vacancies filling, etc).

Rubidium Fluoride Modified SnO2 for Planar n‐i‐p Perovskite Solar Cells

“…For example, recently Nogueira and co‐workers reported that Rb + binds to interstitial halogen (I i and Br i ) defects at the grain boundaries, resulting in a reduced deep traps density by the formation of shallower states. [ 52 ] In addition, theoretical research also demonstrated that the deep traps can be reduced by alkali metals in contact with interstitial halide defects. [ 53 ] For these reasons, we conclude that the decreased trap density should be attributed to the Rb + cations, including those locating at the interface and in the bulk perovskite.…”

Layered metal halide perovskite solar cells: A review from structure‐properties perspective towards maximization of their performance and stability

“…Alkali metal cations might also be explored to assist in the passivation of defects in both A and A' sites. Our group developed a post‐synthetic method of passivation that might be suitable to passivate 2D‐PSCs: the use of rubidium butyrate as a passivating agent may effectively passivate both cation vacancies (V A and V A’ ) and surface halide vacancies (V X ) 208 . Another advantage in using this passivation method is that the organic acylate can be chosen to match the aryl/alkylammonium backbone of the separators (e.g., butyrate/butylammonium), so that its introduction when passivating halides vacancies would be less disturbing to the crystal structure.…”

A Coadditive Strategy for Blocking Ionic Mobility in Methylammonium‐Free Perovskite Solar Cells and High‐Stability Achievement

“…[ 18,19 ] However, the full elimination of MA + must be targeted for a better stabilization. [ 20–33 ] The most popular approach for MA‐free PSCs consists in replacing MA + by Cs + and/or by Rb + cations, two alkali metals. [ 20,21,31–33 ] Several authors have developed interfacial engineering for boosting the performances of the devices.…”

“…[ 20,21,31–33 ] Several authors have developed interfacial engineering for boosting the performances of the devices. [ 22–24,33 ] However, in the absence of MA, PSCs usually show inferior PCEs due to an insufficient quality of the PVK material. Increasing the material crystallinity and passivating defects must be targeted.…”