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

June 22, 2015 // By Paul Buckley
Researchers at KIT in Germany are claiming to have developed for the first time a functioning organic solar cell consisting of a single component has been produced from metal-organic framework compounds (MOFs).

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.