Local Crystal Misorientation Influences Non-Radiative Recombination

TL;DR

This study demonstrates that local crystal misorientation and strain within perovskite grains significantly influence non-radiative recombination, affecting the material's optoelectronic properties.

Contribution

It introduces ultrasensitive EBSD mapping combined with photoluminescence to correlate local crystal misorientation with non-radiative recombination in perovskite films.

Findings

Higher local strain correlates with increased non-radiative recombination.

Larger grains tend to have greater orientation spread and strain.

Optical PL is anticorrelated with local grain misorientation.

Abstract

We use ultrasensitive electron backscatter diffraction (EBSD) to map the local crystal orientations, grains, and grain boundaries in CH3NH3PbI3 (MAPI) perovskite thin films. Although the true grain structure is broadly consistent with the morphology visible in scanning electron microscopy (SEM), the inverse pole figure maps taken with EBSD reveal grain structure and internal misorientation that is otherwise hidden. Local crystal misorientation is consistent with the presence of local strain which varies from one grain to the next. We acquire co-aligned confocal optical photoluminescence (PL) microscopy images on the same MAPI samples used for EBSD. We correlate optical and EBSD data, showing that PL is anticorrelated with the local grain orientation spread, suggesting that grains with higher degrees of crystalline orientational heterogeneity (local strain) exhibit more non-radiative recombination. We find that larger grains tend to have larger grain orientation spread, consistent with higher degrees of strain and non-radiative recombination.