Probing Ferroelectricity in Hybrid Halide Perovskites through Tunneling Spectroscopy

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Ferroelectricity in methylammonium lead iodide (MAPbI₃) is debated due to overlapping ionic and ferroelastic effects.
• Distinguishing true ferroelectricity requires advanced nanoscale probing techniques.

Purpose of the Study:

• To definitively probe ferroelectricity in MAPbI₃ films.
• To differentiate ferroelectric polarization from ion migration and ferroelasticity.
• To establish new methods for analyzing dipole-mediated functionalities.

Main Methods:

• Utilized scanning tunneling microscopy (STM) to measure voltage-induced tunneling current.
• Employed Kelvin probe force microscopy (KPFM) to detect surface potential changes.
• Applied voltage poling to induce and observe polarization dynamics.

Main Results:

• Observed poling-dependent tunneling current in STM.
• Detected a reversible surface potential flip in KPFM, indicating remnant nanoscale polarization.
• Provided compelling evidence for ferroelectricity in unstrained MAPbI₃ films.

Conclusions:

• Ferroelectricity in MAPbI₃ is confirmed, independent of ion migration and ferroelasticity.
• STM and KPFM are powerful tools for probing nanoscale polarization.
• Findings facilitate the integration of polarization phenomena into perovskite optoelectronics.