From the Terminator to Spiderman's suit, self-repairing robots and devices
abound in sci-fi movies. In reality, though, wear and tear reduce the
effectiveness of electronic devices until they need to be replaced. What is
the cracked screen of your mobile phone healing itself overnight, or the
solar panels providing energy to satellites continually repairing the damage
caused by micro-meteorites?
The field of self-repairing materials is rapidly expanding, and what used to
be science fiction might soon become reality, thanks to Technion—Israel
Institute of Technology scientists who developed eco-friendly nanocrystal
semiconductors capable of self-healing. Their findings, recently published
in Advanced Functional Materials, describe the process, in which a group of
materials called double perovskites display self-healing properties after
being damaged by the radiation of an electron beam. The perovskites, first
discovered in 1839, have recently garnered scientists' attention due to
unique electro-optical characteristics that make them highly efficient in
energy conversion, despite inexpensive production. A special effort has been
put into the use of lead-based perovskites in highly efficient solar cells.
The Technion research group of Professor Yehonadav Bekenstein from the
Faculty of Material Sciences and Engineering and the Solid-State Institute
at the Technion is searching for green alternatives to the toxic lead and
engineering lead-free perovskites. The team specializes in the synthesis of
nano-scale crystals of new materials. By controlling the crystals'
composition, shape, and size, they change the material's physical
properties.
Nanocrystals are the smallest material particles that remain naturally
stable. Their size makes certain properties more pronounced and enables
research approaches that would be impossible on larger crystals, such as
imaging using electron microscopy to see how atoms in the materials move.
This was, in fact, the method that enabled the discovery of self-repair in
the lead-free perovskites.
The perovskite nanoparticles were produced in Prof. Bekenstein's lab using a
short, simple process that involves heating the material to 100°C for a few
minutes. When Ph.D. students Sasha Khalfin and Noam Veber examined the
particles using a transmission electron microscope, they discovered the
exciting phenomenon. The high voltage electron beam used by this type of
microscope caused faults and holes in the nanocrystals. The researchers were
then able to explore how these holes interact with the material surrounding
them and move and transform within it.
They saw that the holes moved freely within the nanocrystal, but avoided its
edges. The researchers developed a code that analyzed dozens of videos made
using the electron microscope to understand the movement dynamics within the
crystal. They found that holes formed on the surface of the nanoparticles,
and then moved to energetically stable areas inside. The reason for the
holes' movement inwards was hypothesized to be organic molecules coating the
nanocrystals' surface. Once these organic molecules were removed, the group
discovered the crystal spontaneously ejected the holes to the surface and
out, returning to its original pristine structure—in other words, the
crustal repaired itself.
This discovery is an important step towards understanding the processes that
enable perovskite nanoparticles to heal themselves, and paves the way to
their incorporation in solar panels and other electronic devices.
Reference:
Sasha Khalfin et al, Self‐Healing of Crystal Voids in Double Perovskite
Nanocrystals Is Related to Surface Passivation, Advanced Functional
Materials (2021).
DOI: 10.1002/adfm.202110421