Performance-limiting metastable intragrain impurity nanoclusters in metal halide perovskites.

Area of Science:

• Materials Science
• Renewable Energy
• Nanotechnology

Background:

• Impurity control is vital for high-efficiency and stable perovskite solar cells.
• Existing research primarily focuses on grain boundary and interface impurities.
• Intragrain (sub-)nanoscale impurities remain largely unexplored.

Purpose of the Study:

• To reveal and characterize nanoscale impurities within perovskite grains.
• To understand the impact of these intragrain impurities on optoelectronic properties and stability.
• To develop strategies for mitigating these impurities and improving device performance.

Main Methods:

• Low-dose scanning transmission electron microscopy (STEM) for imaging intragrain nanoclusters.
• First-principles calculations to analyze the nature and effects of impurities.
• Quasi-in situ observations to study impurity behavior over time.
• Solution processing with incorporated inner salts to reduce nanocluster formation.

Main Results:

• Identified previously unknown, metastable orthorhombic non-perovskite phase nanoclusters within grains.
• Demonstrated that these intragrain nanoclusters degrade optoelectronic properties and chemical stability.
• Successfully reduced nanocluster density through inner salt incorporation.
• Achieved enhanced perovskite solar cell device performance.

Conclusions:

• Intragrain nanoclusters represent a critical, previously overlooked impurity source in perovskite films.
• Understanding and controlling these unconventional impurities is key for fundamental advancements.
• This work opens new avenues for nano-engineering improved perovskite solar cells and optoelectronic devices.