Neutrons reveal twinning in halide perovskites

• A great 10 years back, study groups uncovered the class of semi-organic halide perovskites, which are currently making a rapid career as brand-new products for solar cells. The combined organic-inorganic semiconductors accomplished efficiencies of over 25 percent within a few years.

They take their name from their fundamental structure, which is really similar to that of the mineral perovskite (CaTiO3), however includes other parts: halide anions, lead cations and organic molecular cations.

In the case of one of the most vital compound of the course, methylammonium lead iodide CH3NH3PbI3 (typically abbreviated as MAPI), which was additionally examined below, the molecular cations are methylammonium cations and also the anions are iodide anions.

Although greater than 4000 publications on halide perovskites have actually shown up in 2019 alone, it has not yet been feasible to fully recognize their structure. When it comes to MAPI this was attributed, to name a few things, to the reality that they are generated as polycrystalline films at elevated temperature and it was thought that twinning occurs when they are cooled to room temperature level.

The development of doubles is intricate as well as can considerably transform the material homes. It is consequently exciting to investigate this procedure more closely.

"We have actually now crystallised MAPI at area temperature and evaluated the crystals therefore created with the Laue cam Falcon on BER II," says Dr. Joachim Breternitz, HZB.

Along with his colleagues Prof. Susan Schorr as well as Dr. Michael Tovar, he was able to establish from the data that crystals expanded at room temperature also develop twins. This offers a brand-new insight into the formation as well as development procedure of MAPI. "Our outcomes suggest that the crystallisation nuclei have a greater symmetry than the mass crystals," explains Breternitz.

With these insights, the synthesis of the highly important thin movies can be specifically optimised.

The neutron source BER II has given neutrons for research study until its scheduled closure in December 2019. "This was one of our last experiments at FALCON on BER II and also I hope that we had the ability to make helpful payments right as much as the end," claims Breternitz.