knjiga solarna energija dobra

642 CADMIUM TELLURIDE SOLAR CELLS
10 −6
10 −7
Diffusion coefficient
[cm 2 /s]
10 −8
10 −9
10 −10
10 −11
Boundary
Bulk
10 −12
10 −13 0 5 10 15 20 25 30 35
CdCl 2 partial pressure
[mTorr]
10 −5
10 −6
Diffusion coefficient
[cm 2 /s]
10 −7
10 −8
10 −9
10 −10
10 −11
Boundary
Bulk
10 −12
10 −13 0 100 200 300 400 500 600 700 800
Oxygen partial pressure
[Torr]
Figure 14.18 Sensitivity of bulk and grain-boundary diffusion coefficients (a) to pCdCl 2 at constant
pO 2 ∼125 Torr, at T = 420 ◦ C, and (b) to pO 2 at constant pCdCl 2 = 9 mTorr, at T = 420 ◦ C
from the differences in current generation, device operation is fundamentally similar for
cells with differing amounts of CdTe 1−x S x alloy in the absorber layer.
14.3.4 Back Contact
The top region shown in Figure 14.7 is the back contact, consisting of a primary contact
to CdTe, which typically consists of a tellurium-containing p + surface, and a secondary
contact, which is the current-carrying conductor. As with other p-type semiconductors,
there is a tendency to form a Schottky barrier with many metals, and achieving a lowresistance
ohmic contact has proven to be challenging. The most common strategy is
to form a Te-rich surface by selective chemical etching and then apply copper or a