Photovoltaic Power Generation - Renewable Energy: Technology, Economics and Environment - page 255

Front contact Front contact Front contact

a) a)

Superstrate Superstrate Superstrate

1. Structuring step 1. Structuring step

b) b)

Absorber Absorber

c) c)

2. Structuring step 2. Structuring step

d) d)

Rear contact Rear contact

e) e)

3. Structuring step 3. Structuring step

f) f)

Fig. 6.13 Layer deposition and structure sequence of a photovoltaic thin film module
(a) deposition of the transparent front electrode on the glass superstrate; b) first structuring
step; c) deposition of the photovoltaic active absorber layer; d) second structuring step;
e) deposition of the rear electrode; f) third structuring step)

Solar cells for concentrating photovoltaic systems. Solar cells of concentrating
photovoltaic systems are illuminated up to 500 times more at standard test condi-
tions (STC) compared to fixed mounted cells. However, at higher radiation con-
centrations the serial resistance constitutes a major problem due to the high cur-
rents. This is why concentrator cells must be especially highly doped and be pro-
vided with low-loss contacts /6-27/.
Terrestrial concentrating photovoltaic systems are almost exclusively provided
with silicon-based solar cells, whose structure is similar to that of the highly effi-
cient silicon solar cells mentioned above. On a laboratory scale, they reach elec-
trical efficiencies of up to 29 % at 140-fold concentration of the radiation.
Furthermore, concentrator cells based on gallium arsenic (GaAs) and ternary
III-V alloys, partly assembled as tandem structures have been investigated. With
regard to epitactically grown mono-crystalline tandem structures, efficiencies of
up to 34 % have been reported for 100 to 300-fold concentrations.
For such concentrator systems it is of particular importance to avoid high tem-
peratures, which will cause power losses. Further more it has to be taken into
consideration that high concentration factors, in the range of several 100's, do
need a two axis tracking system and only direct radiation can be used.

Dye solar cells made of nano-porous titan oxide (TiO 2 ). Electrochemical solar
cells made of nano-porous titan oxide (TiO 2 ) use a TiO 2 particles layer of a typical