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Metal-organic framework compounds: The future for flexible solar cells?

Metal-organic framework compounds: The future for flexible solar cells?

Technology News |
By eeNews Europe



The material is elastic and could also be used for the flexible coating of clothes and deformable components.

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 interest of researchers, because their functionality can be adjusted by varying the components. “A number of properties of the material can be changed,” explained Wöll. 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. The porphyrine-based MOFs have 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 haemoglobin 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).

“This new application of metal-organic framework compounds is the beginning only. The end of this development line is far from being reached,” said Professor Christof Wöll, Director of KIT Institute of Functional Interfaces (IFG)

The researchers expect that the photovoltaic capacity of the material may be increased 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,” expalined Wöll. Thanks to their mechanical properties, MOF thin films of a few hundred nanometers in thickness can be used for flexible solar cells 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 n alternative to silicon that has to be processed at high costs before it can be used for the photoactive layer of a solar cell.

Reference
Jinxuan Liu, Wencai Zhou, Jianxi Liu, Ian Howard, Goran Kilibarda, Sabine Schlabach, Damien Coupry, Matthew Addicoat, Satoru Yoneda, Yusuke Tsutsui, Tsuneaki Sakurai, Shu Seki, Zhengbang Wang, Peter Lindemann, Engelbert Redel, Thomas Heine, and Christof Wöll: ‘Photoinduzierte Erzeugung von Ladungsträgern in epitaktischen MOF-Dünnschichten: hohe Leistung aufgrund einer indirekten elektronischen Bandlücke?’, Angewandte Chemie, Ausgabe 25/2015. German edition: DOI: 10.1002/ange.201501862, International edition: DOI: 10.1002/anie.201501862

Related articles and links:

www.kit.edu

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