Civil Engineering Reference
In-Depth Information
this structure the SWNT allows a pathway for the electrons to travel along
(Kymakis
et al.
, 2003). Unfortunately, this is currently very ineffi cient and
issues with the combination of the NTs are still occurring, leaving the way
open for further improvements.
Another approach is to use CNT as a transparent electrode to replace
the currently used indium tin oxide (ITO) which could solve issues with its
lack of compatibility with polymers, poor mechanical properties, expensive
production costs and material cost and availability. Currently the option of
ITO over CNT provides comparable effi ciency but again more work is
required to make it a practical option.
Finally, one further option to enhance the fl ow of current between the
cells is to use graphene as a possible electrode, again as an alternative to
ITO. Graphene offers an inexpensive, transparent and fl exible omnipresent
carbon substrate in a fl at chicken-wire form with the major problem to date
being the joining of the graphene to the panel due to it not accepting water
solutions. However, it has been suggested by Park
et al.
(2010) that this issue
could be overcome by doping the cell surface, hence including impurities,
which in turn enables the graphene to be accepted. Added to this is the fact
that the overall conductivity is improved and this could in theory solve
some of the issues seen in the previous generation, offering a lightweight,
fl exible, transparent PV cell, thus leading the way to other PV installation
options.
Research has discussed many aspects related to carbon nanotubes. Not
only can they be combined with polymers and bucky balls, which is a hollow
spherical module completely made of carbon, to form a painted PV product,
the NT can also be coated by both p and n type semiconductors which
provides a p-n junction for electricity generation. In 2002 SWNT and
polymer PV devices were seen to provide a doubled photocurrent, but this
was not the last advancement, rather the start of this development. Also the
substrates which the CNT are placed on are currently polyethylene tere-
phthalate, glass, polymethyl methacrylate and silicon, but this research is
only in the primary stages and could be further expanded. A specifi c
example is naphthalocyanine (NaPc) dye-sensitized nanotubes which use
nanotubes as electrons and polymer as holes and provide increased absorp-
tion of both red and ultraviolet as well as larger short circuit current
(Kymakis and Amaratunga, 2003). It is not only the quantum dot that
enables more output from the electron; the NT also offers this possibility.
Work is ongoing and, in 2011, the University of Surrey Advanced Tech-
nology Institute published work on the combination of organic solar cells
and MWNT, showing that both SWNT and MWNT are progressing (Miller
et al.
, 2006). Also the development of the CNT will include matching to the
related solar spectrum, improved optical absorption and the reduction of
carrier scattering. To date there are three main production methods for
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