Mapping Surface-Defect and Ions Migration in Mixed-Cation Perovskite Crystals

Area of Science:

• Materials Science
• Solid-State Physics
• Photovoltaics

Background:

• Single crystal perovskites are promising for optoelectronic devices.
• Surface properties significantly impact perovskite performance, but are often overlooked.
• Understanding charge carrier dynamics at the nanoscale is crucial.

Purpose of the Study:

• To investigate the role of cation composition in surface defect formation and charge carrier dynamics.
• To correlate ion migration with surface passivation and device performance.
• To explore advanced techniques for probing nanoscale phenomena in perovskites.

Main Methods:

• Utilized 4D ultrafast scanning electron microscopy (4D-USEM) to study photogenerated carrier transport within the top nanometers.
• Employed density functional theory (DFT) to analyze defect centers and ion migration pathways.
• Investigated two mixed-cation perovskite compositions: FA_0.6MA_0.4PbI₃ and FA_0.4MA_0.6PbI₃.

Main Results:

• FA_0.6MA_0.4PbI₃ exhibited longer charge carrier lifetimes than FA_0.4MA_0.6PbI₃, attributed to higher surface defect density.
• DFT calculations confirmed lower energy barriers for iodide ion migration to the surface in higher FA content samples.
• Ion migration effectively passivates surface vacancies, leading to fewer defects and prolonged carrier lifetimes.

Conclusions:

• Cation selection critically influences charge carrier transport and defect formation in single crystal perovskites.
• Controlling ion migration is essential for managing surface vacancies and enhancing optoelectronic device performance.
• This study highlights the importance of nanoscale surface characterization for advancing perovskite technology.