Environmental Engineering Reference
In-Depth Information
Figure 4.1
A shematic diagram of the glass/conducting glass (metal-
1)/CdS/CdTe/metal-2devicestructureaccordingtothesimplep-njunction
model.
the n-CdS layer, and suitable electrical contacts such as Au, Cu/Au,
Cu/NiorNiserveastheohmiccontactstothep-typeCdTelayer.The
energy banddiagram ofsuch a device is shown in Fig. 4.2.
A large number of research groups has worked on glass/
conducting glass (CG)/CdS/CdTe/metal structures, depositing low-
cost CdS and CdTe semiconducting layers, on glass/CG substrates.
The CG used is usually indium tin oxide (ITO) or fluorine-doped
tin oxide (FTO) with metallic conduction and over 90% light
transparency. In principle, any transparent conducting layer with
high transparency of light and low sheet resistance for electrical
conduction can be used in these devices. The CdS layer used is
always n-type, and various growth methods such as chemical bath
deposition (CBD), electrodeposition, spray pyrolysis, and vacuum
evaporation have been used to produce this window layer. The
thickness of the CdS window layer varies from 80 nm to a few
microns according to the work reported in the literature. The
absorber layer, CdTe, has also been produced using a variety of
methods such as the close-space sublimation technique (CSST),
electrodeposition, and screen printing. The thickness of the CdTe
layer varies in the range 1.5-5.0
μ
m, and a typical device may
contain a 0.1
μ
mCdSand
2.0
μ
m CdTe layers. The fabrication
processforthecompletesolarcellalsoincludeschemicaltreatment,
∼
