13
Thin-film solar cells
In Chapter 12 we discussed the PV technology based on c-Si wafers, which currently is by
far the dominant PV technology. It is very likely that it will stay dominant for a long time.
In this chapter we will look at an alternative family of technologies, namely thin-film
technologies, also referred to as the second generation PV technology. These solar cells
are made from films that are much thinner than the wafers that form the base for first
generation PV. According to Chopra et al. [50], ‘a thin film is a film that is created ab
initio by the random nucleation process of individually condensing/reacting
atomic/ionic/molecular species on a substrate. The structural, chemical, metallurgical and
physical properties of such a material are strongly dependent on a large number of
deposition parameters and may also be thickness dependent.’
Thin-film solar cells were expected to become much cheaper than first generation
solar cells. However, due to the current price decline in wafer-based solar cells, thin-film
solar cells have not yet become economically viable.
1 In general thin-film cells have a
lower efficiency than c-Si solar cells, with GaAs being an exception to this rule of thumb
[47]. In contrast to wafer-based silicon solar cells, which are self-supporting, thin-film
solar cells require a carrier that gives them mechanical stability. Usual carrier materials are
glass, stainless steel or polymer foils. It is thus possible to produce flexible thin-film solar
cells.
In thin-film solar cells the active semiconductor layers are sandwiched between a
transparent conductive oxide (TCO) layer and the electric back contact. Often a back
reflector is introduced at the back of the cell in order to minimize transmissive solar cell
losses. As we will see in this chapter, many different semiconductors are used for thin-film
solar cells. Figure 13.1 shows the abundance of elements in the Earth’s crust. Some
semiconductors require very rare elements such as indium (In), selenium (Se), or tellurium
(Te). For terawatt scale photovoltaics, solar cells should be based on abundant elements
only.
Thin-film solar cells
In Chapter 12 we discussed the PV technology based on c-Si wafers, which currently is by
far the dominant PV technology. It is very likely that it will stay dominant for a long time.
In this chapter we will look at an alternative family of technologies, namely thin-film
technologies, also referred to as the second generation PV technology. These solar cells
are made from films that are much thinner than the wafers that form the base for first
generation PV. According to Chopra et al. [50], ‘a thin film is a film that is created ab
initio by the random nucleation process of individually condensing/reacting
atomic/ionic/molecular species on a substrate. The structural, chemical, metallurgical and
physical properties of such a material are strongly dependent on a large number of
deposition parameters and may also be thickness dependent.’
Thin-film solar cells were expected to become much cheaper than first generation
solar cells. However, due to the current price decline in wafer-based solar cells, thin-film
solar cells have not yet become economically viable.
1 In general thin-film cells have a
lower efficiency than c-Si solar cells, with GaAs being an exception to this rule of thumb
[47]. In contrast to wafer-based silicon solar cells, which are self-supporting, thin-film
solar cells require a carrier that gives them mechanical stability. Usual carrier materials are
glass, stainless steel or polymer foils. It is thus possible to produce flexible thin-film solar
cells.
In thin-film solar cells the active semiconductor layers are sandwiched between a
transparent conductive oxide (TCO) layer and the electric back contact. Often a back
reflector is introduced at the back of the cell in order to minimize transmissive solar cell
losses. As we will see in this chapter, many different semiconductors are used for thin-film
solar cells. Figure 13.1 shows the abundance of elements in the Earth’s crust. Some
semiconductors require very rare elements such as indium (In), selenium (Se), or tellurium
(Te). For terawatt scale photovoltaics, solar cells should be based on abundant elements
only.