First solar cell made of highly ordered molecular frameworks

June 19, 2015, Karlsruhe Institute of Technology
First solar cell made of highly ordered molecular frameworks
Organic solar cells made of metal-organic frameworks are highly efficient in producing charge carriers. Credit: Wöll/KIT

Researchers at KIT have developed a material suited for photovoltaics. For the first time, a functioning organic solar cell consisting of a single component has been produced on the basis of metal-organic framework compounds (MOFs). The material is highly elastic and might also be used for the flexible coating of clothes and deformable components. This development success is presented on the front page of the journal Angewandte Chemie International Edition.

"We have opened the door to a new room," says Professor Christof Wöll, Director of KIT Institute of Functional Interfaces (IFG). "This new application of metal-organic framework compounds is the beginning only. The end of this development line is far from being reached," the physicist emphasizes.

Metal-organic frameworks, briefly called MOFs, consist of two basic elements, metal node points and organic molecules, which are assembled to form microporous, crystalline materials. For about a decade, MOFs have been attracting considerable interest of researchers, because their functionality can be adjusted by varying the components. "A number of properties of the material can be changed," Wöll explains. So far, more than 20,000 different MOF types have been developed and used mostly for the storage or separation of gases.

The team of scientists under the direction of KIT has now produced MOFs based on porphyrines. These porphyrine-based MOFs have highly interesting photophysical properties: Apart from a high efficiency in producing charge carriers, a high mobility of the latter is observed. Computations made by the group of Professor Thomas Heine from Jacobs University Bremen, which is also involved in the project, suggest that the excellent properties of the solar cell result from an additional mechanism – the formation of indirect band gaps – that plays an important role in photovoltaics. Nature uses porphyrines as universal molecules e.g. in hemoglobin and chlorophyll, where these organic dyes convert light into chemical energy. A metal-organic solar cell produced on the basis of this novel porphyrine-MOF is now presented by the researchers in the journal Angewandte Chemie (Applied Chemistry). The contribution is entitled "Photoinduzierte Erzeugung von Ladungsträgern in epitaktischen MOF-Dünnschichten: hohe Leistung aufgrund einer indirekten elektronischen Bandlücke?" (photo-induced generation of charge carriers in epitactic MOF-thin layers: high efficiency resulting from an indirect electronic band gap?).

"The clou is that we just need a single in the solar cell," Wöll says. The researchers expect that the photovoltaic capacity of the material may be increased considerably in the future by filling the pores in the crystalline lattice structure with molecules that can release and take up electric charges.

By means of a process developed at KIT, the crystalline frameworks grow in layers on a transparent, conductive carrier surface and form a homogeneous thin film, so-called SURMOFs. "The SURMOF process is suited in principle for a continuous manufacturing process and also allows for the coating of larger plastic carrier surfaces," Wöll says. Thanks to their mechanical properties, MOF thin films of a few hundred nanometers in thickness can be used for flexible or for the coating of clothing material or deformable components. While the demand for technical systems converting sunlight into electricity is increasing, organic materials represent a highly interesting alternative to silicon that has to be processed at high costs before it can be used for the photoactive layer of a solar cell.

Explore further: Researchers develop new method to produce metal-organic frameworks

More information: "Photoinduced Charge-Carrier Generation in Epitaxial MOF Thin Films: High Efficiency as a Result of an Indirect Electronic Band Gap?" Angew. Chem. Int. Ed., 54: 7441–7445. doi: 10.1002/anie.201501862

Related Stories

Free pores for molecule transport

July 31, 2014

Metal-organic frameworks (MOFs) can take up gases similar to a sponge that soaks up liquids. Hence, these highly porous materials are suited for storing hydrogen or greenhouse gases. However, loading of many MOFs is inhibited ...

Recommended for you

Interfacing with the brain

June 15, 2018

The nervous system is loaded with encoded information: thoughts, emotions, motor control. This system in our bodies is an enigma, and the more we can do to understand it, the more we can do to improve human life. Brain-machine ...

Electronic skin stretched to new limits

June 15, 2018

An electrically conductive hydrogel that takes stretchability, self-healing and strain sensitivity to new limits has been developed at KAUST. "Our material outperforms all previously reported hydrogels and introduces new ...

Researchers can count on improved proteomics method

June 15, 2018

Every cell in the body contains thousands of different protein molecules and they can change this composition whenever they are induced to perform a particular task or convert into a different cell type. Understanding how ...

Modern alchemists are making chemistry greener

June 14, 2018

Ancient alchemists tried to turn lead and other common metals into gold and platinum. Modern chemists in Paul Chirik's lab at Princeton are transforming reactions that have depended on environmentally unfriendly precious ...

This is what a stretchy circuit looks like

June 14, 2018

Researchers in China have made a new hybrid conductive material—part elastic polymer, part liquid metal—that can be bent and stretched at will. Circuits made with this material can take most two-dimensional shapes and ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

Straw_Cat
not rated yet Jun 20, 2015
I had to look up the word 'clou': in this case it means "a major point of interest or attention." (a noun) and comes from the Latin, either directly or indirectly from >clavus< =nail.
In French clou now mean 'nail'.

http://dictionary...wse/clou

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.