Quantitative Analysis of Light Induced Ion Segregation in Mixed-Halide Perovskites

TL;DR

This study introduces a method to analyze halide ion distribution and strain in mixed-halide perovskites under illumination, revealing ion segregation dynamics relevant for solar cell efficiency.

Contribution

A novel approach combining x-ray scattering and strain calculations to investigate halide segregation in mixed-halide perovskites during illumination.

Findings

Halide ions segregate into Br-rich and I-rich regions under light.

The distribution of ions can be quantitatively determined from scattering data.

Segregation relaxes in the dark, restoring initial ion distribution.

Abstract

Mixed-halide perovskites (MHPs) offer good band gap tunability by stoichiometry changes, which is an essential property for the creation of multijunction solar cells. However, under illumination, halide ions in MHP segregate and create I- and Br-rich regions, which decreases the efficiency of potential solar cells. In this work, a method for a detailed investigation of the distribution of halide ions within the MHP during and after illumination is introduced. Calculations of the strain field created by the halide segregation were performed, and the obtained local displacement of atoms was used to calculate the x-ray diffuse scattering. By fitting the experimental data measured on the thin polycrystalline layer of FA0.83Cs0.17Pb(I0.6Br0.4)3 the distribution of Br- and I- ions within an illuminated MHP was determined and the subsequent relaxation process of the segregation in the dark was tracked. Creation of highly Br-rich regions within slightly I-rich volume during the illumination was observed.