# Flexoelectric domain walls enable charge separation and transport in cubic perovskites

## TL;DR

This paper explains how perovskites efficiently separate and transport charges using flexoelectric fields at domain walls, resolving a key paradox in their performance.

## Contribution

The study reveals that flexoelectric polarization at domain walls enables efficient charge separation and transport in perovskites.

## Key findings

- Flexoelectric fields at domain walls spatially separate electrons and holes, suppressing recombination.
- Domain walls act as mesoscopic transport channels for long-lived photocarriers.
- Structural heterogeneity is linked to enhanced optoelectronic performance in perovskites.

## Abstract

The exceptional energy-harvesting efficiency of lead-halide perovskites arises from unusually long photocarrier diffusion lengths and recombination lifetimes that persist even in defect-rich, solution-grown samples. Paradoxically, perovskites are also known for having very short exciton decay times. Here, we resolve this apparent contradiction by showing that key optoelectronic properties of perovskites can be explained by localized flexoelectric polarization confined to interfaces between domains of spontaneous strain. Using birefringence imaging, electrochemical staining, and zero-bias photocurrent measurements, we visualize the domain structure and directly probe the associated internal fields in nominally cubic single crystals of methylammonium lead bromide. We demonstrate that localized flexoelectric fields spatially separate electrons and holes to opposite sides of domain walls, exponentially suppressing recombination. Domain walls thus act as efficient mesoscopic transport channels for long-lived photocarriers, microscopically linking structural heterogeneity to charge transport and offering mechanistically informed design principles for perovskite solar-energy technologies.

Rak et al. report the visualisation of internal domain boundaries in perovskite single crystals, revealing that electric fields produced by localised flexoelectricity separate electric charges, reducing recombination of charge carriers, and leading to long-lived photocurrent under zero bias.