Ionic and electronic polarization effects in horizontal hybrid perovskite device structures close to equilibrium

Area of Science:

• Materials Science
• Solid-State Physics
• Device Physics

Background:

• Hybrid perovskites exhibit significant electrical responses due to mobile ionic defects, impacting device functionality, performance, and stability.
• Interpreting polarization effects and quantifying ionic conductivity in mixed ionic-electronic conductors like perovskites presents challenges, even under equilibrium conditions.

Purpose of the Study:

• To investigate the electrical response of methylammonium lead iodide (MAPI) devices under near-equilibrium conditions.
• To clarify the interpretation of DC polarization and impedance spectroscopy measurements in hybrid perovskite devices.
• To understand the role of mixed conductivity and device geometry in the electrical behavior of MAPI.

Main Methods:

• Experimental investigation of horizontal MAPI devices near equilibrium.
• Analysis of DC polarization and impedance spectroscopy measurements in the dark.
• Utilizing equivalent circuit models to interpret impedance spectra, accounting for mixed conductivity and device geometry.

Main Results:

• Polarization in MAPI devices is well-described by mixed conductor/metal interface charging, with a Debye length around 1 nm.
• A distinct impedance signature at intermediate frequencies indicates ionic diffusion parallel to the MAPI/contact interface.
• Analysis rules out significant iodine exchange with the gas phase, highlighting the role of intrinsic ionic species.

Conclusions:

• The study clarifies the measurement and interpretation of mixed conductivity and polarization in hybrid perovskites.
• Findings are relevant for characterizing and developing perovskite-based transistors, memristors, and solar cells.
• Provides insights into the behavior of mixed ionic-electronic conducting materials.