Press Release 015/2021

Shedding Light on Perovskite Films

Efficient Materials for Future Solar Cells – New Model to Determine Photoluminescence Quantum Efficiency
2021_015_Perowskit-Schichten genau beleuchtet_72dpi
In terms of efficiency, perovskite solar cells have caught up on silicon solar cells, but some of their properties are not yet understood completely. (Photo: Markus Breig, KIT)

Perovskite semiconductors are considered promising materials for solar cells of the next generation. Suitability of a semiconductor for photovoltaics is reflected among others by the so-called photoluminescence quantum efficiency. Researchers of Karlsruhe Institute of Technology (KIT) have now developed a model, by means of which photoluminescence quantum efficiency of perovskite films can be determined exactly for the first time. This is reported in Matter (DOI: 10.1016/j.matt.2021.01.019).

Photovoltaics decisively contributes to sustainable energy supply. The efficiency of solar cells in directly converting light energy into electrical energy depends on the material used. Metal-halide perovskites are considered very promising materials for solar cells of the next generation. With these semiconductors named after their special crystal structure, a considerable increase in efficiency was achieved in the past years. Meanwhile, perovskite solar cells have reached an efficiency of up to 25.5 percent, which is quite close to that of silicon solar cells that are presently dominating the market. Moreover, the materials needed for perovskite solar cells are rather abundant. The solar cells can be produced easily and at low cost and they can be used for various applications. The theoretically achievable efficiency of perovskite solar cells is about 30.5 percent.

To approach this value, optoelectronic quality of perovskite semiconductors must be further increased. In principle, materials suited for photovoltaics are expected to not only absorb light, but to also emit it efficiently. This process is known as photoluminescence. The corresponding parameter, photoluminescence quantum efficiency, is perfectly suited to determine the quality of perovskite semiconductors. Together with scientists from the Center for Advanced Materials (CAM) of Heidelberg University and the Technical University of Dresden, researchers of KIT’s Institute of Microstructure Technology (IMT) and Light Technology Institute (LTI) have now developed a model, by means of which photoluminescence quantum efficiency of perovskite films can be determined reliably and exactly for the first time. Their results are reported in Matter.

Materials Have More Optimization Potentials than Assumed

Eine wichtige Rolle bei der Berechnung der Photolumineszenz-Quantenausbeute spielt der Anteil des sogenannten Photonen-Recyclings, der Reemission von reabsorbierten Photonen. (Abbildung/Foto: IMT/KIT)

When calculating photoluminescence quantum efficiency, the share of so-called photon recycling, the re-emission of re-absorbed photons, plays an important role. (Photo: IMT/KIT) ((Initiale/Recycelte Photolumineszenz (PL) = Initial / recycled photoluminescence (PL); Direkt emittierte PL = Directly emitted PL; Gestreute PL = Scattered PL)) 

“With the help of our model, photoluminescence quantum efficiency under solar irradiation can be determined far more precisely,” says Dr. Paul Fassl from IMT. “Photon recycling is of high importance. This is the share of photons emitted by the perovskite, which is re-absorbed and re-emitted in the thin films.” The researchers applied their model to methylammonium lead triiodide (CH3NH3PbI3), one of the perovskites of highest photoluminescence quantum efficiency. So far, it has been estimated to amount to about 90 percent. Model calculations, however, revealed that it is about 78 percent. The scientists explain that previous estimations did not adequately consider the effect of light scattering and, hence, underestimated the probability of photons – the quantums of light energy – leaving the film before they are re-absorbed. “Our results show that the potential for optimization of these materials is far higher than assumed,” says Dr. Ulrich W. Paetzold, Head of the Advanced Optics and Materials for Next Generation Photovoltaics Group of IMT. The team offers an open-source application based on the model, by means of which photoluminescence quantum efficiencies of various perovskite materials can be calculated. 

Original Publication

Paul Fassl, Vincent Lami, Felix J. Berger, Lukas M. Falk, Jana Zaumseil, Bryce S. Richards, Ian A. Howard, Yana Vaynzof, Ulrich W. Paetzold: Revealing the internal luminescence quantum efficiency of perovskite films via accurate quantification of photon recycling. Matter. Cell Press, 2021. DOI: 10.1016/j.matt.2021.01.019.

More about the KIT Energy Center:

Being “The Research University in the Helmholtz Association”, KIT creates and imparts knowledge for the society and the environment. It is the objective to make significant contributions to the global challenges in the fields of energy, mobility, and information. For this, about 10,000 employees cooperate in a broad range of disciplines in natural sciences, engineering sciences, economics, and the humanities and social sciences. KIT prepares its 22,800 students for responsible tasks in society, industry, and science by offering research-based study programs. Innovation efforts at KIT build a bridge between important scientific findings and their application for the benefit of society, economic prosperity, and the preservation of our natural basis of life. KIT is one of the German universities of excellence.

or, 23.02.2021

Margarete Lehné
Chief Press Officer (acting)
Phone: +49 721 608-41105
Fax: +49 721 608-43658
presse does-not-exist.kit edu

Contact for this press release:

Sandra Wiebe
Press Officer
Phone: +49 721 608-41172
sandra wiebe does-not-exist.kit edu
The photo in the best quality available to us may be requested by
presse does-not-exist.kit edu or phone: +49 721 608-41105.