Wednesday, December 05, 2012

A Solar Cell All Made From Carbon.

The first solar cell has been reported, whose active components all consist of forms of carbon Until 1985, there were just two known allotropes of carbon - diamond and graphite - but in that year the fullerenes were added to the list. The latter are also known as "buckyballs", in honour of Buckminster Fuller, who conceived the structure of the geodesic dome, which these materials mimic at the molecular level. Since then, nanotubes and graphene have been discovered, all pure carbon, but with different atomic arrangements that determine their particular structures and properties, which include a high electrical conductivity. In the cell, carbon nanotubes are used to provide a light-absorber and electron donor, while a counterpart electron acceptor is fashioned from the fullerene, C60. This photo-active double layer is made the filling of a sandwich between a reduced graphene oxide anode and doped carbon nanotubes to act as the cathode. Among the advantages claimed for this device are low cost, ready availability of materials and simple processing from solution - using wet chemistry methods.

Other workers have previously used carbon nanotubes, graphene and fullerenes in various styles of solar cells, but this is apparently the first time that all three carbon allotropes have been used in the same cell. Most solar cells are transparent to near infra-red wavelengths, and hence around half the solar spectrum is unusable by them as an energy source. In contrast, the carbon cells adsorb near IR radiation strongly, and it is thought that it might be possible to combine them into a tandem cell, e.g. with silicon, to absorb sunlight right across the solar spectrum, resulting in greater power production. However, the light-to-electricity conversion efficiency is, as yet, extremely low, at 0.06%. By way of comparison, 12% might be got from a dye-based solar cell, and as much as 25% from crystalline semiconductors. A typical silicon solar panel gives around 15%. Thus, there is some way to go before the all-carbon solar cell is used in anger.


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