Fair-weather power: Solar textiles

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  • Published: Aug 15, 2014
  • Author: David Bradley
  • Channels: X-ray Spectrometry
thumbnail image: Fair-weather power: Solar textiles

Coaxial approach

Integrating Perovskite Solar Cells into a Flexible Fiber Credit: Wiley VCH

Whether you're a tweed-wearing hipster or down with the kids sporting your post-modern baggy jeans, textile-based solar cells that could be patched into your clothes might one day let you charge up your mobile phone or other gadgets while out in the sunshine, according to research published this month in the journal Angewandte Chemie. The work by scientists in China used X-ray characterization of key components to take the first solar strides.

Huisheng Peng of the Department of Macromolecular Science and Laboratory of Advanced Materials at Fudan University, China and colleagues focus on functional composite materials and their energy applications. He and co-workers created aligned carbon nanotube/polymer composites and developed novel fiber-shaped solar cells, Li-ion batteries and electrochemical supercapacitors. However, it is the potential applications of perovskite, the latest "wonder" material that has caught their eye this time and more critically the possibility of weaving composite fibres based on this material into textiles for solar-powered fabrics, that might be used in baggage, tents and clothing for personal, leisure and even military applications.

Flexible power

The team has developed flexible, coaxial cells based on a composite of perovskite and carbon nanotubes. Conversion efficiencies are around 3.3 percent which considered "excellent" compared to previous attempts at coaxial solar fibres. Moreover, they would have low production costs for fabricating at relatively low cost into products. This is in stark contrast to conventional solar cells which are either inexpensive and inefficient or have usable efficiency at a high cost.

Perovskite materials, compounds sharing the crystal structure of their archetype the mineral calcium titanium oxide (titanate), are far less costly than silicon and other crystalline semiconductors; they also work without a range of equally costly additives. The perovskites are commonly semiconductors themselves and absorb light relatively efficiently. Most importantly, they can move electrons excited by light for long distances within the crystal lattice before they return to their energetic ground state and take up a solid position - a property that is very important in solar cells. As such, earlier this year researchers demonstrated how a double layer of mesoporous titanium dioxide and zirconium dioxide built on a perovskite scaffold could achieve solar energy conversion efficiencies of 12.8 percent for more than one thousand hours under full sunlight. Peng and colleagues used a relatively simple and inexpensive production process, in solution to fabricate their multi-layered solar power fibres.

The hole solution

The anode is a fine stainless steel wire coated with a compact n-semiconducting titanium dioxide layer. They deposited a layer of porous nanocrystalline titanium dioxide on to this giving them a large surface area on which to then deposit their perovskite material in this case an amino lead iodide compound. An organic coating of spiro-OMeTAD (2,2′,7,7′-tetrakis(N,N′-di-p-methoxyphenylamine)-9,9′-spirobifluorene) is then wrapped in a transparent layer of aligned carbon nanotubes which are continuously wound over the length of the fibre to act as the cathode. OMeTAD is considered one of the most promising "hole conductors" for solar energy conversion.

The team explains that the perovskite layer absorbs light, which excites electrons leading to charge separation between the electrons and the formally positively charged “holes”. The electrons enter the conducting band of the compact titanium dioxide layer and move to the anode. The “holes” are captured by the organic layer of OMeTAD. It is the large surface area and the high electrical conductivity of the carbon nanotube cathode that facilitate the rapid conduction of the charges with high photoelectric currents, the team says giving it the high efficiency they record.

"We will try to further enhance the power conversion efficiency that remains much lower than their planar counterparts," Lee told SpectroscopyNow. "In addition, we will also try to develop some general and effective routes to scale up the production. We hope, in a few years, these fibre-shaped solar cells start to be used in our life, for instance, being woven into clothes to power some micro-electronic devices.

Related Links

Angew Chem Int Edn, 2014, online: "Integrating Perovskite Solar Cells into a Flexible Fiber"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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