Buried Interface Ionic Engineering Enables Defect Passivation and Efficient Cu₂AgBiI₆ Solar Cells.

Area of Science:

• Materials Science
• Renewable Energy
• Solid-State Chemistry

Background:

• Lead-free perovskite-inspired materials like copper bismuth iodide (Cu$_{2}$AgBiI$_{6}$, CABI) offer sustainable alternatives for photovoltaics.
• Microscopic loss mechanisms currently limit the performance of CABI-based solar cells.

Purpose of the Study:

• To investigate the microscopic loss mechanisms in CABI films.
• To develop a passivation strategy to enhance CABI solar cell performance.

Main Methods:

• Depth-resolved chemical profiling to analyze film composition.
• First-principles calculations and Density Functional Theory (DFT) to study defect behavior.
• Fabrication and characterization of CABI solar cells with a buried interface treatment.

Main Results:

• Observed depth-dependent copper distribution in CABI films, indicating mobility and redistribution.
• Identified copper vacancies (V$_{Cu}$) as deep recombination centers.
• Demonstrated that a buried KCl interface layer passivates V$_{Cu}$ defects, enhancing device performance.

Conclusions:

• Copper mobility and V$_{Cu}$ defects are key loss mechanisms in CABI.
• Buried interface ionic passivation with KCl is an effective strategy to improve CABI solar cells.
• This approach shows potential for other multicomponent ionic semiconductors.