Ferroelastic Hysteresis in Thin Films of Methylammonium Lead Iodide

TL;DR

This study investigates ferroelastic hysteresis in methylammonium lead iodide thin films, revealing how strain, domain interactions, and domain wall stability influence material properties and degradation.

Contribution

It provides the first detailed characterization of ferroelastic hysteresis and domain behavior in MAPbI3 thin films using GIWAXS, linking strain states to material stability and degradation.

Findings

Ferroelastic hysteresis involves stable domain structures in MAPbI3 films.

Domain wall mobility is limited over time, affecting stability.

Strain-induced nucleation of domain walls correlates with film degradation.

Abstract

Mechanical strain can modify the structural and electronic properties of methylammonium lead iodide MAPbI3. The consequences of ferroelastic hysteresis, which involves the retention of structural memory upon cycles of deformation, in polycrystalline thin films of MAPbI3 are reported. Repeatedly bent films of MAPbI3 on flexible polyimide substrates were examined using Grazing Incidence Wide-Angle X-ray Scattering (GIWAXS) to quantitatively characterize the strain state, populations, and minimum sizes of twin domains. Approximate locations for the coercive stress and saturation on the ferroelastic stress-strain curve are identified, and domains from differently-strained twin sets in the films are found to interact with each other. The presence of specific twin domains is found to correlate to reports of the heterogeneity of strain states with defect content. Long-term stability testing reveals that domain walls are highly immobile over extended periods. Nucleation of new domain walls occurs for specific mechanical strains and correlates closely with degradation of the films. These results help to explain the behavior of ion migration, degradation rate, and photoluminescence in thin films under compressive and tensile strain.