Civil Engineering Reference
In-Depth Information
Sunlight
High
Eg
1
Cell 1
Middle
Eg
2
Cell 2
Low
Eg
3
Cell 3
Eg
1
> Eg
2
> Eg
3
12.5
Operation of a three-layer multijunction PV.
Table 12.7
Multilayer PV layers
Max theoretical power
conversion effi ciency (%)
Layer
Band gap (eV)
Notes
1
1.13
33.7
Energy below and above
red are lost
2
1.64
44
0.94
3
1.83
48
1.16
0.71
Infi nity
Undefi ned
64
Estimation
times the energy, is not absorbed as the band gap is too low - this is an issue
under research, hence the interest in multi-junctions. Table 12.7 outlines
four different layers and the possible theoretical effi ciency with each high-
lighting the band gaps that they include.
The second part of the third generation focuses on the development of
nanostructures, which obviously are in the size of nanometres. It must be
understood that there are vast differences between normal and nanostruc-
tures because at that small scale the quantum physical effect takes over the
device. The most important feature of the nanostructure is that their optical
features change as the size varies providing the option of changing the
optical properties by optimizing the size of the nanostructure. This provides
many more options with regard to how the capture of the photons can be
optimized, enabling more of the energy of the solar spectrum to be used,
thus providing maximum effi ciency.
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