Imaging Light‐Induced Migration of Dislocations in Halide Perovskites with 3D Nanoscale Strain Mapping

Abstract

In recent years, halide perovskite materials have been used to make high performance solar cell and light‐emitting devices. However, material defects still limit device performance and stability. Here, we use synchrotron‐based Bragg Coherent Diffraction Imaging to visualise nanoscale strain fields, such as those local to defects, in halide perovskite microcrystals. We find significant strain heterogeneity within MAPbBr3 (MA = CH3NH3+) crystals in spite of their high optoelectronic quality, and identify both 〈100〉 and 〈110〉 edge dislocations through analysis of their local strain fields. By imaging these defects and strain fields in situ under continuous illumination, we uncover dramatic light‐induced dislocation migration across hundreds of nanometers. Further, by selectively studying crystals that are damaged by the X‐ray beam, we correlate large dislocation densities and increased nanoscale strains with material degradation and substantially altered optoelectronic properties assessed using photoluminescence microscopy measurements. Our results demonstrate the dynamic nature of extended defects and strain in halide perovskites, which will have important consequences for device performance and operational stability.This article is protected by copyright. All rights reserved

Strain Heterogeneity and Extended Defects in Halide Perovskite Devices

“…Though further studies are required to confirm this hypothesis, contact potential difference, current/voltage, and photoluminescence measurements suggest such aerosol post-treatments reduce defect densities and prolong film performance. 26,28,63 The observation that dislocation formation is a key feature of beam damage in MAPbBr 3 25 is consistent with the supposition that dislocation annihilation through improved processing enhances halide perovskite performance.…”

“…23 Ferroelastic domain structures have also been identified in CsPbBr 3 halide perovskite nanoparticles with BCDI, 24 and our recent study employed the technique to track the increased dislocation migration in MAPbBr 3 microcrystals in response to visible light illumination. 25 Here, by performing BCDI measurements on Cs 0.1 FA 0.9 Pb-(I 0.95 Br 0.05 ) 3 and Cs 0.15 FA 0.85 SnI 3 (FA = CH(NH 2 ) 2 ) halide perovskites in full device stacks, we find large (up to ca. 1%) intragrain strains with root-mean-squared local strain values of up to ca.…”

Single‐Step Chemical Vapor Deposition of Methyl Ammonium Lead Halide Perovskite for p–i‐n Solar Cells

“…We assume that continuous UV‐exposure accelerated the formation of the mid‐gap light‐activated trap and accumulation at the interfaces. We can also argue that this could be partially explained by the presence of charged line defects, such as dislocations, for which movement under the illumination in halide perovskites was reported just recently [41] . Also, the dislocations in halide perovskites can carry and electric charge and could significantly affect the device performance.…”

A novel radical-reaction interruption strategy for enhancing the light stability of perovskite solar cells

“…The migration of ions in perovskite materials is widely believed to induce variations in doping density and built-in potential, thereby initiating local lattice distortion and potentially compromising structural stability. 12,13 The illumination or bias, in particular, exacerbates ion migration within a perovskite film, which has been directly observed at the macro scale using optical and atomic force microscopy. 14,15 Due to lower migration activation energy ( E a ), halogen anions (I − ) and organic cations (FA + or MA + ) in perovskites easily migrate along point defects, resulting in their preferential accumulation at the electrodes under illumination or bias conditions.…”