Perovskite materials: Neutrons show twinning in halide perovskites


Date:
October 13, 2020
Source:
Helmholtz-Zentrum Berlin fu"r Materialien und Energie
Summary:
Solar cells based on hybrid halide perovskites achieve high
efficiencies.

These mixed organic-inorganic semiconductors are usually produced as
thin films of microcrystals. An investigation with the Laue camera
at the neutron source BER II could now clarify that twinning occurs
during crystallisation even at room temperature. This insight is
helpful for optimising production processes of halide perovskites.



FULL STORY ==========================================================================
A good ten years ago, research teams discovered the class of semi-organic halide perovskites, which are now making a rapid career as new materials
for solar cells. The mixed organic-inorganic semiconductors achieved efficiencies of over 25 percent within a few years. They take their
name from their basic structure, which is very similar to that of the
mineral perovskite (CaTiO3), but contains other components: halide anions,
lead cations and organic molecular cations.


==========================================================================
In the case of the most important compound of the class, methylammonium
lead iodide CH3NH3PbI3 (usually abbreviated as MAPI), which was also
studied here, the molecular cations are methylammonium cations and the
anions are iodide anions. Although more than 4000 publications on halide perovskites have appeared in 2019 alone, it has not yet been possible to
fully understand their structure. In the case of MAPI this was attributed, among other things, to the fact that they are produced as polycrystalline
films at elevated temperature and it was assumed that twinning occurs
when they are cooled to room temperature.

The formation of twins is complex and can significantly change the
material properties. It is therefore exciting to investigate this process
more closely.

"We have now crystallised MAPI at room temperature and analysed the
crystals thus formed with the Laue camera Falcon on BER II," says
Dr. Joachim Breternitz, HZB. Together with his colleagues Prof. Susan
Schorr and Dr.

Michael Tovar, he was able to determine from the data that crystals grown
at room temperature also form twins. This gives a new insight into the crystallization and growth process of MAPI. "Our results indicate that
the crystallisation nuclei have a higher symmetry than the bulk crystals," explains Breternitz.

With these insights, the synthesis of the technologically important thin
films can be specifically optimised.

The neutron source BER II has provided neutrons for research until
its scheduled shutdown in December 2019. "This was one of our last
experiments at FALCON on BER II and I hope that we were able to make
useful contributions right up to the end," says Breternitz.


========================================================================== Story Source: Materials provided by Helmholtz-Zentrum_Berlin_fu"r_Materialien_und_Energie.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Joachim Breternitz, Michael Tovar, Susan Schorr. Twinning in
MAPbI3 at
room temperature uncovered through Laue neutron
diffraction. Scientific Reports, 2020; 10 (1) DOI:
10.1038/s41598-020-73487-1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201013124121.htm

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