Resolving Nanoscale Heterogeneities in Lead Halide Perovskites Through Low-Dose Concurrent 4D-STEM-EDX Mapping

Area of Science:

• Materials Science
• Nanotechnology
• Renewable Energy

Background:

• Mixed-cation lead mixed-halide perovskites are promising for photovoltaics.
• These materials can exhibit instabilities due to nanoscale heterogeneity.
• Characterizing these instabilities requires high-resolution techniques like transmission electron microscopy (TEM).

Purpose of the Study:

• To develop a low-dose methodology for characterizing perovskite films without inducing damage.
• To map the chemical and structural architecture of perovskite films at the nanoscale.
• To understand the origins of structural instabilities in mixed-halide perovskites.

Main Methods:

• Developed a low-dose, concurrent methodology using four-dimensional scanning transmission electron microscopy (4D-STEM).
• Utilized energy-dispersive x-ray spectroscopy (EDX) for chemical mapping.
• Correlated chemical composition with crystal structure at the nanoscale.

Main Results:

• Revealed a complex mosaic of coexisting crystal structures in a (FA0.83Cs0.17)Pb(I0.8Br0.2)3 perovskite film.
• Established a direct link between local chemical composition and crystal structure.
• Identified local cesium deficiencies as the primary driver for the formation of inactive hexagonal polytypes.

Conclusions:

• Local cesium deficiencies are a fundamental origin of structural instabilities in mixed-composition perovskite thin-films.
• Nanoscale compositional homogeneity is crucial for achieving long-term device performance in perovskite solar cells.
• The developed low-dose 4D-STEM/EDX methodology is essential for studying electron-beam sensitive materials.