13.3.4
The typical precursor gas for depositing the Si films is silane (SiH 4 ), often diluted
with hydrogen (H 2 ). The precursor gases are brought into the process chamber at low
pressure. In plasma-enhanced chemical vapour deposition (PECVD), a radio frequency
(RF) or very high frequency (VHF) bias voltage between two electrodes is used to
generate a plasma, which leads to dissociation of the SiH 4 atoms into radicals such as
SiH 3 , SiH 2 or SiH. These radicals react with the substrate, where a layer is growing. By
increasing the H 2 content, the material becomes more nanocrystalline, as sketched in
Figure 13.13.
As precursors for the doping, diborane (B 2 H 6 ) is mainly used for the p layers and
phosphine (PH 3 ) for the n layers. For silicon carbide layers, in addition to the silane,
methane (CH 4 ) is used. Silicon oxide layers can be made by combining silane with carbon
dioxide (CO 2 ).
After the p-i-n junction is deposited, the sample is covered with a mask, which
defines the areas onto which the metallic back contacts are to be deposited. In Delft, silver
is deposited with evaporation. Little pieces of silver are put in a boat that is heated by a
very high current flowing through it. The silver melts and evaporated silver particles can
move freely through a vacuum until they hit the sample, where a silver layer is deposited.
This process is explained in more detail in Chapter 14.
Now the solar cells are ready – every metallic square defines a little solar cell. The
small metal strip is the front contact and the back of the metallic square is the electric back
contact. Naturally, such a configuration is not suitable for large-scale thin-film PV
modules. The production of thin-film modules is discussed in Chapter 15.
Crystalline silicon thin-film solar cells
We conclude the section on thin-film silicon technology with a brief discussion on
crystalline silicon thin-film solar cells. The aim is to combine the advantages of crystalline
silicon technology and thin-film silicon technology [74] by using high-quality crystalline
films of only several tenths of micrometres thickness as absorbers. These films are
positioned on a substrate or a superstrate.
Different approaches are investigated for reaching this goal: Kerf-less wafering
techniques are investigated where thin wafers can be prepared without any kerf loss. The
wafers are then transferred onto a glass substrate. With this technique, efficiencies of
10.0% were obtained with a 50 μm thick absorber [74].
Alternatively, films of large grain nanocrystalline silicon or amorphous silicon can be
deposited. The amorphous films can be crystallized after deposition. This crystallization
The typical precursor gas for depositing the Si films is silane (SiH 4 ), often diluted
with hydrogen (H 2 ). The precursor gases are brought into the process chamber at low
pressure. In plasma-enhanced chemical vapour deposition (PECVD), a radio frequency
(RF) or very high frequency (VHF) bias voltage between two electrodes is used to
generate a plasma, which leads to dissociation of the SiH 4 atoms into radicals such as
SiH 3 , SiH 2 or SiH. These radicals react with the substrate, where a layer is growing. By
increasing the H 2 content, the material becomes more nanocrystalline, as sketched in
Figure 13.13.
As precursors for the doping, diborane (B 2 H 6 ) is mainly used for the p layers and
phosphine (PH 3 ) for the n layers. For silicon carbide layers, in addition to the silane,
methane (CH 4 ) is used. Silicon oxide layers can be made by combining silane with carbon
dioxide (CO 2 ).
After the p-i-n junction is deposited, the sample is covered with a mask, which
defines the areas onto which the metallic back contacts are to be deposited. In Delft, silver
is deposited with evaporation. Little pieces of silver are put in a boat that is heated by a
very high current flowing through it. The silver melts and evaporated silver particles can
move freely through a vacuum until they hit the sample, where a silver layer is deposited.
This process is explained in more detail in Chapter 14.
Now the solar cells are ready – every metallic square defines a little solar cell. The
small metal strip is the front contact and the back of the metallic square is the electric back
contact. Naturally, such a configuration is not suitable for large-scale thin-film PV
modules. The production of thin-film modules is discussed in Chapter 15.
Crystalline silicon thin-film solar cells
We conclude the section on thin-film silicon technology with a brief discussion on
crystalline silicon thin-film solar cells. The aim is to combine the advantages of crystalline
silicon technology and thin-film silicon technology [74] by using high-quality crystalline
films of only several tenths of micrometres thickness as absorbers. These films are
positioned on a substrate or a superstrate.
Different approaches are investigated for reaching this goal: Kerf-less wafering
techniques are investigated where thin wafers can be prepared without any kerf loss. The
wafers are then transferred onto a glass substrate. With this technique, efficiencies of
10.0% were obtained with a 50 μm thick absorber [74].
Alternatively, films of large grain nanocrystalline silicon or amorphous silicon can be
deposited. The amorphous films can be crystallized after deposition. This crystallization