Ruddlesden-Popper Defects Act as a Free Surface: Role in Formation and Photophysical Properties of CsPbI₃

Area of Science:

• Materials Science
• Solid-State Physics
• Renewable Energy

Background:

• Cesium lead iodide (CsPbI3) perovskites show promise for solar cells due to their ideal bandgap.
• Phase stability and high power conversion efficiency in CsPbI3 solar cells are significant challenges.
• Ruddlesden-Popper (RP) defects are present in CsPbI3 but their formation and impact are poorly understood.

Purpose of the Study:

• Investigate the formation and impact of RP defects in CsPbI3 thin films.
• Elucidate the role of RP defects in CsPbI3 phase stability and photophysical properties.
• Propose strategies for optimizing RP defects to enhance solar cell performance.

Main Methods:

• Vapor deposition of CsPbI3 thin films with varying Cs-excess.
• Electron microscopy for analyzing defect structures.
• Density functional theory (DFT) calculations for electronic properties.

Main Results:

• Increased Cs-excess led to a higher prevalence of RP defects, improved structural stability, and reduced photophysical properties.
• Electron microscopy revealed RP defect atomic positions resemble free surfaces, indicating a phase stabilization role.
• DFT calculations showed RP planes are electronically benign, but antisites at turning points are detrimental.

Conclusions:

• RP defects play a crucial role in CsPbI3 phase stabilization.
• Optimizing RP defect structures by increasing RP planes and reducing turning points is proposed for enhanced solar cell performance.
• The revealed formation mechanism of RP defects may be applicable to other perovskite systems.