Rahul Dewan - Jacobs University

5. µC-SI SOLAR CELLS WITH TRIANGULAR TEXTURE
Q u a n tu m E ffic ie n c y , A b s o rp tio n
1 .0
0 .8
0 .6
0 .4
0 .2
S i p -la y e r
µc -S i:H
i-la y e r Q E
Z n O
F ro n t T C O
0 .0
3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 9 0 0 1 0 0 0 1 1 0 0
W a v e le n g th [n m ]
Figure 5.6: External quantum efficiency of the 1000 nm thick p-i-n microcrystalline
silicon solar cell and parasitic absorptions in the silicon p-layer and front zinc oxide
layer. Period and height of the triangular texture were 700 nm and 400 nm, respectively.
The absorptions in the n-layer silicon and back zinc oxide are not shown since
they are almost negligible.
wavelengths (from 300 nm to 500 nm), whereas the layer is almost transparent for
the longer wavelengths. Absorption loss in the front zinc oxide layer for shorter wavelengths
accounts for almost 50%. For wavelengths ranging from 500 nm to 750 nm, the
absorption in the front zinc oxide is minimized. Optical loss in the aluminum-doped
front zinc oxide layer for longer wavelengths increases as a result of the free carrier
absorption. From Fig. 5.6, information on the total reflection of the solar cell structure
can also be extracted. The reflection can be simply calculated by R=1-A, where
A is the total absorption of the solar cell. The white area in Fig. 5.6 represents the
total reflection from the solar cell. It can be observed that for the longer wavelengths,
a major portion of the incident energy is lost as reflection. Our studies on different
thicknesses of the i-layer has shown that reduction of the reflection should be the key
point in optimizing thinner solar cells. Detailed description of those results are given
in Chapter 7.
5.4 Summary
Light trapping and incoupling of light in thin-film microcrystalline silicon solar cells
with periodic triangular profiles was investigated. Compared to that of a solar cell
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