Redox-active ions unlock substitutional doping in halide perovskites

Area of Science:

• Materials Science
• Solid-State Physics
• Semiconductor Research

Background:

• Electrical doping is crucial for advancing metal halide perovskites (MPHs) in electronics.
• Methylammonium lead iodide (CH₃NH₃PbI₃) is a promising semiconductor material.
• Efficient doping methods are needed to unlock the full potential of MPHs.

Purpose of the Study:

• To demonstrate n-type doping of methylammonium lead iodide (CH₃NH₃PbI₃).
• To investigate the use of samarium (Sm²⁺) as a post-fabrication dopant.
• To analyze the impact of doping on the material's electrical properties and crystal structure.

Main Methods:

• Post-fabrication introduction of Sm²⁺ into CH₃NH₃PbI₃.
• X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) for dopant incorporation analysis.
• X-ray Diffraction (XRD) to assess crystal structure and phase separation.
• Mott-Schottky analysis to determine charge carrier density.
• Variable-temperature conductivity measurements.

Main Results:

• Successful n-type doping of CH₃NH₃PbI₃ via Sm²⁺ oxidation to Sm³⁺.
• Conductivity increased by nearly 3 orders of magnitude.
• No phase separation observed at low/medium doping concentrations.
• Fermi level shifted to 0.52 eV, indicating n-type doping.
• Charge carrier density estimated at ~10¹⁷ cm^-3.
• Partial dopant ionization observed at room temperature due to freeze-out.

Conclusions:

• Sm²⁺ is an effective dopant for achieving n-type conductivity in CH₃NH₃PbI₃.
• The doping mechanism involves Sm²⁺ oxidation, releasing negative charge.
• This method offers a promising route for fabricating efficient perovskite-based electronic devices.
• Further research into dopant ionization at different temperatures is warranted.