1.
2.
3.
4.
5.
6.
7.
8.
10.4
1.
2.
3.
10.4.1
represent particular losses in energy conversion:
due to non-absorption of long wavelengths;
due to thermalization of the excess energy of photons;
due to the total reflection;
by incomplete absorption due to the finite thickness;
due to recombination;
by metal electrode coverage, shading losses;
due to voltage factor;
due to fill factor.
Design rules for solar cells
Now, as we have extensively discussed all the factors that limit the efficiency of a solar
cell we are able to distil three design rules. We will use these design rules in Part III when
we discuss different PV technologies. The three design rules are:
utilization of the band gap energy,
spectral utilization,
light management.
We will now take a closer look at each of these design rules.
Bandgap utilization
As we have seen earlier in this chapter, the open circuit voltage V oc is always below the
voltage V G corresponding to the bandgap. This loss is characterised with the bandgap
utilization efficiency η V . The open circuit voltage is determined by the extent to which the
quasi-Fermi levels are able to split, which is limited by the charge carrier-recombination
mechanisms. We discussed the different recombination mechanisms already in detail in
Chapter 7. Here, we briefly summarise them and discuss how they affect the bandgap
utilization.
Figure 10.8 shows a p-n junction, with the p-doped region on the left and the n-doped
region on the right. Further, the quasi-Fermi levels are depicted. The extent of splitting
between the quasi-Fermi levels determines the open circuit voltage. The open circuit
2.
3.
4.
5.
6.
7.
8.
10.4
1.
2.
3.
10.4.1
represent particular losses in energy conversion:
due to non-absorption of long wavelengths;
due to thermalization of the excess energy of photons;
due to the total reflection;
by incomplete absorption due to the finite thickness;
due to recombination;
by metal electrode coverage, shading losses;
due to voltage factor;
due to fill factor.
Design rules for solar cells
Now, as we have extensively discussed all the factors that limit the efficiency of a solar
cell we are able to distil three design rules. We will use these design rules in Part III when
we discuss different PV technologies. The three design rules are:
utilization of the band gap energy,
spectral utilization,
light management.
We will now take a closer look at each of these design rules.
Bandgap utilization
As we have seen earlier in this chapter, the open circuit voltage V oc is always below the
voltage V G corresponding to the bandgap. This loss is characterised with the bandgap
utilization efficiency η V . The open circuit voltage is determined by the extent to which the
quasi-Fermi levels are able to split, which is limited by the charge carrier-recombination
mechanisms. We discussed the different recombination mechanisms already in detail in
Chapter 7. Here, we briefly summarise them and discuss how they affect the bandgap
utilization.
Figure 10.8 shows a p-n junction, with the p-doped region on the left and the n-doped
region on the right. Further, the quasi-Fermi levels are depicted. The extent of splitting
between the quasi-Fermi levels determines the open circuit voltage. The open circuit