New insights into the structure of organic-inorganic hybrid perovskites

Movie showing the 3D crystal structure as a function of the cell modulation phase. (grey: Pb, brown: Br, black: C, blue: N; white: H) © HZB

10.00 s

In photovoltaics, organic-inorganic hybrid perovskites have made a rapid career. But many questions about the crystalline structure of this surprisingly complex class of materials remain unanswered. Now, a team at HZB has used four-dimensional modelling to interpret structural data of methylammonium lead bromide (MAPbBr3), identifying incommensurable superstructures and modulations of the predominant structure. The study is published in the ACS Journal of Physical Chemistry Letters and was selected by the editors as an Editor's Choice.

Organic-inorganic hybrid perovskites have been intensively investigated for use in solar cells for about ten years. Thin films of such perovskites are inexpensive and already achieve high efficiencies. In addition, they can be perfectly combined with common solar cell materials such as silicon to form tandem cells. At the beginning of 2020, an HZB team was able to achieve a world record efficiency of 29.15 % with a tandem cell made of perovskite and silicon.

But despite the most intensive research, it has not yet been possible to precisely elucidate the crystal structures with their diverse modulations and superstructures as a function of temperature, even for the best-known perovskite compounds such as methylammonium and formamidinium lead halide. 

Now, a team at HZB has analysed structural data of methylammonium lead bromide (MAPbBr3) with a novel model. Postdoc Dr. Dennis Wiedemann used a model that takes a fourth dimension into account in addition to the three spatial dimensions. The structural data were measured at a temperature of 150 Kelvin at the University of Columbia.

"The problem in these hybrid perovskites is the fact that the different modifications do not differ significantly in energy, so that even small temperature differences are sufficient to trigger phase transitions," explains Dr. Joachim Breternitz, co-author of the study. The data on the crystal structure therefore show an average value over many elementary cells, so that modulations and superstructures are not always recognisable. The new model explains the incommensurable superstructures observed in MAPbBr3 in a small temperature window around 150 K, which do not have the same periodicity as the crystal lattice. This complex structure comes from tilts and shifts in the crystal structure. "The new model will also provide more detailed insights into the modulated structures of other perovskite compounds," says Breternitz.


You might also be interested in

  • Stability of perovskite solar cells reaches next milestone
    Science Highlight
    Stability of perovskite solar cells reaches next milestone
    Perovskite semiconductors promise highly efficient and low-cost solar cells. However, the semi-organic material is very sensitive to temperature differences, which can quickly lead to fatigue damage in normal outdoor use. Adding a dipolar polymer compound to the precursor perovskite solution helps to counteract this. This has now been shown in a study published in the journal Science by an international team led by Antonio Abate, HZB. The solar cells produced in this way achieve efficiencies of well above 24 %, which hardly drop under rapid temperature fluctuations between -60 and +80 Celsius over one hundred cycles. That corresponds to about one year of outdoor use.
  • NETZWERKTAG der Allianz für Bauwerkintegrierte Photovoltaik
    NETZWERKTAG der Allianz für Bauwerkintegrierte Photovoltaik
    Der 2. Netzwerktag der Allianz BIPV findet statt am

    10:00 - ca. 16:00 Uhr

    Das HZB, Mitglied in der Allianz BIPV, freut sich, Gastgeber des branchenweiten Austausches zu sein. Neben Praxiserfahrungen von Vertretenden aus Architektur, Fassadenbau und angewandter Forschung steht der direkte Austausch und die Diskussion im Vordergrund.

  • Scientists Develop New Technique to Image Fluctuations in Materials
    Science Highlight
    Scientists Develop New Technique to Image Fluctuations in Materials
    A team of scientists, led by researchers from the Max Born Institute in Berlin and Helmholtz-Zentrum Berlin in Germany and from Brookhaven National Laboratory and the Massachusetts Institute of Technology in the United States has developed a revolutionary new method for capturing high-resolution images of fluctuations in materials at the nanoscale using powerful X-ray sources. The technique, which they call Coherent Correlation Imaging (CCI), allows for the creation of sharp, detailed movies without damaging the sample by excessive radiation. By using an algorithm to detect patterns in underexposed images, CCI opens paths to previously inaccessible information. The team demonstrated CCI on samples made of thin magnetic layers, and their results have been published in Nature.