Improved plasticity in inorganic perovskites
A research team co-led by scholars from City University of Hong Kong has successfully morphed all-inorganic perovskites at room temperature without compromising their functional properties.
All-inorganic lead halide perovskites are becoming increasingly important semiconducting materials in energy conversion and optoelectronics because of their outstanding performance and enhanced environmental stability. The findings were published in Nature Materials.
“However, unlike metal materials or polymers, inorganic semiconductors are often brittle and hard to process. This strongly restricts their applications as optoelectronic products that must withstand mechanical stress and strain without losing their functionality,” said Professor Chen Fu-Rong of the Department of Materials Science and Engineering at CityU who co-led the study.
To overcome this limitation, a research team led by Chen, along with Professor Johnny Ho Chung-yin, Professor Zhao Shijun at CityU, and Professor Lu Yang, now currently working at the University of Hong Kong, explored the deformability of all-inorganic perovskites. They found perovskites can be substantially morphed into distinct geometries at room temperature while preserving their functional properties, an achievement unprecedented in conventional inorganic semiconductors.
In their experiments, the team first synthesized single-crystal micropillars with diameters and widths ranging from 0.4 to 2 μm and lengths of 3 to 10 μm. They then conducted in situ compression experiments with a scanning electron microscope.
They found that under compression, there were continuous slips of partial dislocations on multiple slip systems in the crystal lattice. This domino-like multi-slipping deformation mechanism enabled the micropillars to deform into various distinct shapes without fracturing, including upside-down L shape, Z shape, and wine-glass shape.
With the aid of an atomic-resolution transmission electron microscope (TEM), the team revealed that the atoms in the deformation zone were well connected, leading to undamaged functional properties. “We also observed that the optoelectronic performance of the micropillars remained unaffected by the deformation,” said Ho. “This demonstrates the potential of these materials for use in deformable optoelectronics.”
The research team performed further electronic and structural analyses to uncover the physical origin of this unusual behaviour. “The secret of the morphing ability is the low-slip energy barrier, which ensures facile slips, and the strong Pb–X bonds, which maintain the crystal’s structural integrity and prevent cracking or cleaving,” said Zhao, who specialises in the properties of computational materials. And the bandgap – an energy index influencing the total electrical properties of intrinsic semiconductors – of the crystal lattice remained unchanged after deformation, indicating that the electronic structure of the material was unaffected, he added.
“Our results demonstrated that all-inorganic CsPbX3 single crystals can be substantially deformed and facilely morphed into various shapes through multi-slipping under ambient conditions, without changing their crystalline integrity, lattice structure or optoelectronic properties,” said Chen.
“The underlying mechanism, uncovered by a TEM at the atomic level provides important implications for seeking other intrinsic ductile semiconductors,” he added.