Page 23 - RSE - Results of the Apollon Project

Results of the APolloN PRoject ANd coNceNtRAtiNg PhotovoltAic PeRsPective

tABLE 3. Different approaches developed in the Photovoltaic Community to increase the solar cell effciency value

Approaches under the assumption outlined Approaches which extend in scope beyond the Shockley
by Shockley and Queisser and Queisser limit

Approach Concept Approach Concept
Metamorphic Extending solar cell light absorption by Multiple- Solutions developed to generate with
solar cell adopting slightly lattice mismatched excitation solar one high energy photon (E>>Eg) two or
(MMSC) 12 materials cells (MESC) 13 more electron-hole pairs

Inverted Extending solar cell light absorption by hot-carrier solar Harnessing of hot carries excess
metamorphic adopting slightly lattice mismatched cells (hCSC) 15 kinetic energy, thus avoiding the
solar cell materials and inverting the growth heat dissipation which occurs after
(IMMSC) 14 sequence to reduce the defects in the absorption of high energy photons
active part of the device, by leaving the (E>>Eg)
mismatched materials at the end of the
growth process

Bifacial solar cell Extending solar cell light absorption by up conversion 17 Modifcation of the incident solar
(BFSC) 16 adopting slightly lattice mismatched spectrum so that two low energy
materials and by growing the mismatched photons (with E g
materials on one side of the substrate and give one higher energy photon
the remaining solar cell structure on the (with E>E ) in order to increase light
g
opposite one, in order to leave the defect far absorption
from the active part of the device

Adjustable Optimizing the solar spectrum conversion down Modifcation of the incident solar
Spectrum by using Multijunction III-V based solar conversion 16 spectrum so that a high energy photon
Lattice Matched cell adopting lattice matched dilute nitride (with E>>E ) is converted into several
g
(A-SLAM) materials lower energy photons with energy
solar cells 18 above the band gap to reduce heat
generation in the solar cell
Mechanically Optimizing solar spectrum conversion
stacked or adopting different materials with proper down shifting 20 Modifcation of the incident solar
Semiconductor energy gap which are mechanically stacked spectrum so that high energy photons
bonded solar cells or bonded to avoid the defects commonly are transformed in low energy photons,
(SBSC) 19 found in lattice mismatched semiconductors thus shifting the high energy photons to
spectral region where the solar cell has
a higher quantum effciency

Multi quantum Extending solar cell light absorption by intermediate- Introduction of electronic bands into
well solar cells using Multijunction with multi quantum band solar cells the semiconductor band gap (by adding
(MQWSC) 21 well III-V based heterostructures proper impurities, for example) allowing
for multiple light transition

Figure 12 a), shows that a 37% effcient MJ solar cell working at 500 X has a lower cost per watt than a 44% effcient
MJ solar cell working at 300 X; Figure 12 b) shows that a 37% effcient MJ solar cell obtained with a process yield of
90%, has a lower cost per watt than a 44% effcient MJ solar cell obtained with a process yield of 65%. It follows that
effciency it is not the only parameter which should drive solar cell component development. A simplifed equation
can then be utilized to analyse the weight of the CEPI on the overall CPV system cost:

K K
2
1
CPV System cost = ––––––– + ––––––– + K 3 (1)
CEPI h
c
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