Mimicking nature's solar cells

06 October 2010

US scientists have take inspiration from plants to create a water-based solar cells to convert light into electricity.

Plants efficiently use light to initiate reactions that produce energy in a process known as photosynthesis. Now Orlin Velev and colleagues at North Carolina State University, have created a hydrogel device to mimic this process to create electricity.

The device uses a 98 per cent water hydrogel doped with two photoactive dyes (9,10-dimethoxy-2-anthracenesulfonic acid and ruthenium trisbipyridine).The gel is layered between a copper foil electrode coated with carbon black and graphite and an indium tin oxide-coated plastic substrate serving as the other electrode. The dyes absorb light exciting the electrons into a higher energy state. Transport of the dyes through the hydrogel allows electrons and electron holes to be transferred to the two electrodes completing the circuit and generating a current.

'You don't normally think of water as a component of electric circuits but the human brain is a water-infused gel and so is the green leaf,' says Velev.

Flexible photovoltaic device uses water-based gel to generate electricity from sunlight

The hydrogel based system offers several advantages as the solar cells can bend when built with flexible electrodes, and are made from low cost, eco-friendly materials.

Takashi Nakanishi an expert in organic nanomaterials at the National Institute for Materials Science in Tsukuba, Japan, comments: 'green, flexible, and low-cost are definitely the highly important issues in development of energy conversion devices for the next generation.'

The team went on to replace the artificial photoactive dyes with natural biological complexes, such as cholorphyll, demonstrating that the device works with photoactive biomolecules. These bio-complexes could be key components of environmentally friendly photovoltaics in the future.

Velev admits that there's a long way to go before they can become a practical technology as his solar cells are relatively inefficient; however he hopes they could eventually provide an alternative for the present day solid-state technologies.

'The next step is to mimic the self-regenerating mechanisms found in plants,' says Velev. 'The other challenge is to change the gel and photoactive molecules to improve the efficiency. Eventually the roof of your house could be covered in soft sheets, similar to artificial green leaves, which could generate electricity.'

Russell Johnson


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