Photoinduced iodide repulsion and halides-demixing in layered perovskites

TL;DR

This study uncovers the chemical mechanism behind light-induced halide segregation in layered perovskites, highlighting iodide repulsion and spacer cation roles, which impact device stability and performance.

Contribution

It reveals the chemical process of LIPS in layered and 3D perovskites, emphasizing the role of spacer cations and halide distribution changes under illumination.

Findings

Light induces iodide repulsion and Br-rich phase formation.

LIPS causes halide distribution changes affecting device performance.

Bulk regions exhibit more significant LIPS effects.

Abstract

Mixing halides in metal halide perovskites (MHPs) is an effective approach to adjust MHPs bandgap for applications in tandem solar cells. However, mixed-halide (MH-) MHPs undergo light-induced-phase-segregation (LIPS) under continuous illumination. Therefore, understanding the mechanism of LIPS is necessary for developing stable MH-MHPs. In this work, we investigated LIPS in layered (L) MHPs and discovered a critical role of spacer cations in LIPS. Through probing chemical changes of LIPS, we unveil light-induced-iodide-repulsion and the formation of Br-rich-phase in illuminated regions during LIPS. This discovery also gives insight into LIPS process in three dimensional (3D) MHPs. By further investigating LIPS in 3D MHPs, we reveal that LIPS induces not only the formation of Br-rich and I-rich domains but also an overall change of halide distribution along the film thickness direction, which can affect the electronic energy alignment and consequently MHPs devices performance. Moreover, LIPS is more significant in the bulk due to larger population of photogenerated charge carriers. Overall, this study reveals the chemical mechanism of LIPS in MHPs and its potential effect on device performance, offering insight into understanding LIPS mechanism and improving the stability of MHPs.