Civil Engineering Reference
In-Depth Information
Nanostructures of
semiconductor material
When electronic particles are confined into
small areas by a potential barrier
Material shows
quantization effects
Boundary dimensions
define the output
One dimension
Two dimensions
Three dimensions
Quantum
films/wells
Quantum
wires/rods
Quantum
dots
12.7
Nanostructures and their dimensions.
thousands of atoms. As defi ned in Fig.12.7, QD or nanoparticles are semi-
conducting nanometre-sized crystals (Manna and Mahajan, 2007). There is
still a lot of research ongoing into the various shapes that nanocrystals come
in, but for renewable energy currently the most focus is being placed on
spheres, cubes, rods, wires, tubes and tetrapods. As with the traditional PV
market, QD developers have also decided to consider semiconductor mate-
rials; however, it is not limited to this and research could be completed into
metals or organic materials and they could be combined with porous fi lms
or dyes, but as semiconductors are currently the number one PV material,
this is the obvious starting point. Semiconductor materials are made from
the following mixture of periodic groups: II-VI, III-V and IV-VI.
QDs are expected to be ideal for use in solar panels as they can overcome
one of the previously identifi ed issues of the limited band gap (BG). The
adjustable band gap they offer means that the larger and wider BG equals
more light absorbed which in turn provides more output voltage. A smaller
BG provides more current but less output voltage. Hence to optimize this
phenomenon, ideally tuning the QD to different band gaps would enable
absorption of different wavelengths (Manna and Mahajan, 2007), therefore
removing the previous limited PV effi ciency which is seen with the earlier
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