Flexible approach to energy harvesting

Materials World magazine
1 Jan 2011
Non-transparent film with copper as an electrode. Image courtesy of University of Bolton, UK

Flexible fibres and films with piezoelectric and photovoltaic properties can now harvest natural energy for use in various electrical components, say UK-based researchers.

According to a team at the Institute for Materials Research and Innovation at the University of Bolton, this is the first time that a hybrid photovoltaic-piezoelectric polymer fibre capable of being woven into a fabric has been developed.

Lead researcher, Elias Siores, ascertains that the photovoltaicpiezoelectric film/fibre starts generating energy as soon as it hits the sun, wind, rain or tide.

He explains that a piezoelectric substrate made from either polyvinylidene fluoride, polypropylene, nylon, or polytetrafluoroethylene is deposited with an electrode (aluminium and copper) and laminated. Various layers of organic photovoltaic materials, such as P3HT, PCBM and PEDOT: PSS are then deposited on top by spin coating and thermal evaporation.

‘When the hybrid film/fibre is subjected to mechanical vibrations from wind, rain or tide, the piezoelectric part produces an electrical voltage that is converted to a constant direct current (DC) voltage by a rectifier. The photovoltaic part of the hybrid film produces constant DC voltage from solar energy. The electrical energy can be either used online or can be stored in a battery,’ explains Siores.

He claims there is no delay in the generation of energy once the hybrid material is exposed to the elements.

According to Siores, the initial cost of the organic photovoltaic polymer represents one of the technology’s shortcomings. The major challenges of the research include developing an organic photovoltaic cell outside a controlled atmosphere that does not use harmful materials such as lead, and rare materials, such as indium oxide.

At present, the technology can generate one watt of energy per 20cmx20cm2 of the material. However, the team is currently trying to improve the efficiency of the organic photovoltaic by incorporating carbon nanotubes. It is hoped these will improve the transportation of the electrons to the electrodes, producing higher currents.

Furthermore, he explains, conversion optimisation techniques, via smart microgrid technology, are being developed to enable better energy yield levels.

Other areas of future research include developing technologies and applications based on piezoelectric, photovoltaic, electrorheological and auxetic smart materials for application in medical devices, electronics, personal protection and aerospace.

Brian McCarthy, Sector Leader for the Materials Knowledge Transfer Network (KTN) – Technical Textiles, says, ‘This is really interesting work and shows great promise. A number of groups have tackled solar textiles to power laptops in the desert etc and others have looked at piezo but I believe this is the first time these have been combined’.