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KIT researchers build solar cell from metal-organic frameworks

21 June 2015

Researchers claim a 'world first' for a functioning organic solar cell consisting of a single component based metal-organic framework compounds.

Organic solar cells made of metal-organic frameworks are highly efficient at producing charge carriers (illustration: Wöll/KIT)

Metal-organic frameworks (MOFs) comprise two basic elements - metal node points and organic molecules - which are assembled to form micro-porous, crystalline materials. MOFs have been attracting considerable interest because their functionality can be adjusted by varying these structural components.

“A number of properties of the material can be changed,” says Professor Christof Wöll of the Karlsruhe Institute of Technology (KIT). 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 interesting photo-physical properties, including the efficient production of highly mobile charge carriers.

Work conducted by Professor Thomas Heine's group at Jacobs University, Bremen, which is also involved in the project, suggest that the excellent properties of the new 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; for example, in haemoglobin and chlorophyll, where these organic dyes convert light into chemical energy. The researchers have now developed a metal-organic solar cell on the basis of this novel porphyrine-MOF.

Via a process developed at KIT, the crystalline frameworks grow in layers on a transparent, conductive carrier surface and form a homogeneous thin film or 'SURMOFs'. “The SURMOF process is suitable for continuous manufacturing processes and also allows for the coating of larger plastic carrier surfaces,” says Wöll.

Thanks to their mechanical properties, MOF thin films of a few hundred nanometres in thickness can be used in the construction of flexible solar cells or for the coating of clothing material or deformable components.

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