A UK company that employs 15 people believes it has a product that could help transform solar cell technology from the use of sheets of silicon material mounted in rigid metal frameworks to a roll of a relatively lightweight and flexible material that could be unrolled like carpet for use on curved surfaces or relatively flimsy structures.

Solar cells, the company contends, might find greater use not just in advanced economies, but also as a localized power source in developing countries beset with a limited electricity distribution network and a thirst for electronic devices such as mobile phones.

The Cambridge, England-based company, Eight19, was set up in 2010 to bring to market a concept that originated in the Cavendish Laboratory at Cambridge University. The company’s name is a reference to the time in minutes and seconds that solar energy takes to travel from the Sun to the Earth. Within the last few months, it has made its first sale of a printed plastic “organic photovoltaic” (OPV) material.

PET Project

Dr. Jurjen Winkel, technology manager with the company, says the product is made of a substrate made of PET (polyethylene terepthalate); then an electrode layer that may be ITO (Indium doped tin oxide) or carbon nanotubes; then an electron transport layer; then the photoactive layer itself; then another electron transport layer; and then another electrode layer. Finally a “barrier layer” is included to protect against moisture ingress. This barrier would be a polymeric material that might or might not also incorporate the initial substrate, he says.

The flexible material has a conversion efficiency of around 6%. Image source: National Physical Laboratory.The key physical attribute this sandwich of materials then possesses, says Winkel, is its flexibility, which is the consequence of its cross-section, currently around “300 microns.” In other words, around 0.3mm, although even half that amount should be feasible, he says. Admittedly, its efficiency at converting solar radiation into electrical energy still lags that of its solid silicon counterparts. Winkel says that whereas the efficiency of mainstream solar cells in use today is about 15%, the Eight19 product is about 6%. Crucially, he says, this performance is achieved with a material that is about “one twentieth” the weight of silicon.

Winkel says that in contrast to silicon, the region of the electromagnetic spectrum that is absorbed by an OPV material makes devices made from it suitable for use in areas of low or even artificial light. He says that the product’s efficiency when exposed to LED illumination is about 14% and that only devices using gallium arsenide provide comparable performance. He says the first sale of the Eight19 product is for use in an indoor environment.

The material's apparent suitability for indoor use makes it a potential power source for sensor-rich devices such as light meters or motion detectors in a factory or warehouse. The material itself might be wrapped around the device's exterior housing and connnected to it via a busbar. He says that it might then be necessary to integrate the solar material with a suitably small rechargeable power storage device such as a capacitor.

Printing Process

Eight19 is using a “roll-to-roll” printing process to produce the material in continuous strips 25cm in width. Winkel says that it can, if necessary, cut the material into shapes ready to be integrated with a customer's devices. The production process enables the product to possess a continuous sequence of “serially interconnected cell stripes” in order to provide it with its overall power generation capability.

Nevertheless, if the product is to fulfil its claimed potential as a means of providing a power source in remote areas, then it will need to possess an appropriate degree of physical resilience. Winkel says that testing at the UK's National Physical Laboratory has subjected samples of the material to repeated bending cycles in which the samples have survived being folded in half and back again up to 200 times.

For now, Winkel says that the company will focus on increasing production volumes. Its process currently produces the material at a rate of about two metres per minute, although ramping production by as much as 10 times would help bring down the material’s price, which he says is currently roughly the same as for a silicon counterpart. It would then be for markets to see how the product could best be exploited.