Civil Engineering Reference
In-Depth Information
highlights that there is still work to be done on the creation of junctions,
passivation of defects and connection to silicon cells. One of the real ongoing
problems is linked to spectral sensitivity. Green (2009) also discusses silicon
QD, defi ning the link between changing QD size to control the optical band
gap. Also discussed in this reference is the research that is ongoing into
increasing the voltage by increasing optical BG. The silicon option is expec-
ted to provide not only a higher effi ciency but also a lower cost and it will
also use material that is abundant and, most importantly in this era, envi-
ronmentally friendly. More work on exciton splitting and collection of resul-
ting free electrons and holes could further improve the devices.
An obvious factor also to consider is the materials that could be and are
currently being used in the development of this technology. Materials used
to date include, but are not limited to, cadmium selenide, cadmium sulphide,
cadmium telluride, indium phosphide, indium arsenide, lead selenide and
lead sulphide.
Another example of a QD is a lead selenide semiconductor compound
combined with titanium oxide which is used to remove the hot carriers,
hence enabling new electrons to be embraced. The issue with arrangement
is linked with the fact that, although one wants to induce electronic transfer,
no chemical interaction between the layer/material can be allowed.
In the next few years it is thought that the quantum dot effi ciency could
be increased by not only improving the electrode and layer structure but
also by increasing the QD density. At the start of this century, Nozik pre-
dicted that the use of QDs in PVs would increase effi ciency, enabling 65%
of the sun's energy to be converted into electricity. There have been many
predictions but only time and practical development will truly lay the buil-
ding blocks to future technology.
The size of the QD as discussed previously is a consideration that can
improve effi ciency and so how the size is controlled is important and inclu-
des the following factors:
medium in which they react
reaction temperature
reaction duration.
Therefore the method of QD fabrication is important and currently there
are two main options. The fi rst is the suspension in liquid of ultrafi ne par-
ticles, referred to as colloids. This colloidal chemistry is not expensive and
does not require any expensive equipment; rather it only needs the proper
chemicals and room temperature as a requirement to produce. Basically it
is the linking of one metal ion with another. The second fabrication method
is epitaxial growth. In this process, crystals are grown on a semiconductor
material on the surface of another with the structural orientation being the
same.
Search WWH ::
Custom Search