Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

X-ray vision reveals how polymer solar cells wear out

13.10.2016

Scientists from Technical University of Munich have used the accurate x-ray vision provided by DESY’s radiation source PETRA III to observe the degradation of polymer solar cells. Their study suggests an approach for improving the manufacturing process to increase the long-term stability of such organic solar cells.

Unlike conventional solar cells, which are made of silicon, organic solar cells produce electricity in an active blended layer between two carbon-based materials. When one of these is a polymer, the resulting cell is often referred to as a polymer solar cell. These are particularly promising because they can be manufactured simply and cheaply.


The inner structure of the solar cell’s active layer without (left), with (centre) and after loss of solvent additive (right).

Image: Christoph Schaffer / TUM


Prof. Müller-Buschbaum with his Gruop in the laboratory

Photo: Andreas Heddergott / TUM

They can be used to make extremely lightweight, flexible and even semi-transparent solar cells using printing techniques on flexible polymer materials, opening up completely new fields of application. In general, however, organic solar cells are less efficient than silicon-based ones, and sometimes they have also a reduced lifetime.

Important inner values

The internal structure of the active layer is crucial in organic solar cells. When manufacturing them, the two materials that form the active layer have to separate out of a common solution, much like droplets of oil forming in water.

“It is important that the polymer domains formed in the process are a few tens of nanometres apart,” points out Christoph Schaffer, a PhD student in the Prof. Müller-Buschbaum, Chair for Functional Materials at TU Munich. “Only then positive and negative charge carriers can be efficiently produced in the active layer and separated from each other. If the structure is too coarse or too fine, this no longer happens, and the efficiency of the solar cell will decrease.”

Modern polymer solar cells often consist of so-called low-bandgap polymers, which absorb particularly large amounts of light. In many cases, these require the use of a solvent additive during the manufacturing process in order to achieve high efficiencies. However, this additive is controversial because it might further decrease the lifetime of the solar cells.

X-ray view into the solar cell

The scientists used DESY’s x-ray source PETRA III to study the degradation of such low-bandgap polymer solar cells with solvent additives in more detail. To this end, a solar cell of this type was exposed to simulated sunlight in a chamber, while its key parameters were continuously monitored.

Parallely, the scientists shone a narrowly collimated x-ray beam from PETRA III at the solar cell at different times, providing a picture of the internal structure of the active layer on a nanometre scale every few minutes.

“These measurements can be used to relate the structure to the performance of the solar cell and track it over time,” explains co-author Prof. Stephan Roth, who is in charge of DESY’s P03 beamline, where the experiments were conducted.

“The data reveals that domains that are on the scale of a few tens of nanometres shrink substantially during operation and that their geometric boundaries with other components disappear,” says Schaffer. At the same time, the measurements suggest that the amount of residual solvent additive decreases. The scientists attribute the measured drop in the efficiency of the solar cell to the observed decrease.

“Since there is evidence to suggest that the residual amount of solvent additive decreases, we have to assume that this process can limit the lifetime of the solar cells,” explains Müller-Buschbaum. “Therefore it is essential to come up with strategies for stabilising the structure. This could be achieved through chemical bonding between the polymer chains, or using customised encapsulating substances.”

Size is critical

In an earlier study, the Munich researchers observed the degradation of a different type of polymer solar cell. In that case, the efficiency was found to drop as a result of the active centres gradually growing in size during their operation. This suggested that it is in fact better to manufacture such solar cells with a suboptimal structure, i.e. one that is too fine, so that it can then grow to the optimum size during the first hours of operation.

The current study picks up the story where the previous one left off. “Our first study showed us that the efficiency dropped when the structure became coarser,” says Schaffer. “Exactly the opposite happens in the present study. This behaviour is precisely what we expected, because the composition of the active layer is different.”

“The materials in the first study tend to demix to a high degree,” explains Schaffer. “Here, the opposite is true, and we need the solvent additive in order to achieve the demixing of the materials that is needed to obtain high efficiencies. When the solvent additive disappears during operation, the structure becomes finer and therefore moves away from its optimum.”

Both these studies offer important approaches to optimising the manufacturing of organic solar cells, as co-author Roth points out: “The way these two studies fit together provides a wonderful example of how important synchrotron radiation has become, especially in applied research such as in the field of renewable energies.”

Publication:

Morphological Degradation in Low Bandgap Polymer Solar Cells – An In Operando Study; Christoph J. Schaffer, Claudia M. Palumbiny, Martin A. Niedermeier, Christian Burger, Gonzalo Santoro, Stephan V. Roth, and Peter Müller-Buschbaum
Advanced Energy Materials, 12.10.2016 – DOI: 10.1002/aenm.201600712

Contact:

Prof. Dr. Peter Müller-Buschbaum
Technical University of Munich
Department of Physics, E13
Chair for Functional Materials
James-Franck-Str. 1, 85748 Garching, Germany
Tel.: +49 89 289 12451 – E-mail: muellerb@ph.tum.de

Weitere Informationen:

http://www.functmat.ph.tum.de/
https://www.tum.de/en/about-tum/news/press-releases/short/article/33448/

Dr. Ulrich Marsch | Technische Universität München

Further reports about: PETRA III X-ray X-ray vision nanometres organic solar cells solar cell

More articles from Power and Electrical Engineering:

nachricht How protons move through a fuel cell
22.06.2017 | Empa - Eidgenössische Materialprüfungs- und Forschungsanstalt

nachricht Fraunhofer IZFP acquires lucrative EU project for increasing nuclear power plant safety
21.06.2017 | Fraunhofer-Institut für Zerstörungsfreie Prüfverfahren IZFP

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Quantum thermometer or optical refrigerator?

23.06.2017 | Physics and Astronomy

A 100-year-old physics problem has been solved at EPFL

23.06.2017 | Physics and Astronomy

Equipping form with function

23.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>