110
S. Leu and D. Sontag
therefore these topics fit better into the chapter on Heterojunction (HJT) cells. For
these reasons, this chapter does not deal with cleaning and texturization.
5.2 Cell Processing for the Al-BSF Cell
This section describes the basic steps for manufacturing a solar cell. We describe
first of all the Al-BSF (Aluminium Back Surface Field) cell, which was the most
widely used solar cell until 2015. It was then further developed and led to the PERC
cell, which is described in Sect. 5.3.
5.2.1 Light Trapping by Texturization
The first step in cell production is the Texturization. To get a high efficiency, we
increase the front side of the cleaned, microcrack free and saw damage free wafer surface. We increase the surface area by texturing the wafer. We have already described
this in Chap. 4.
5.2.2 Formation of the pn-Junction
The presence of a charge-separating pn-junction is a prerequisite for a functioning
traditional Al-BSF solar cell. In crystalline solar cells, one employs silicon as a
semiconductor material—with boron and phosphorus as dopants. Silicon is tetravalent, so it has four valence electrons, through which a bond to neighbouring atoms
can be implemented. Boron is trivalent and has, thus, one valence electron missing
compared to silicon, while phosphorus is pentavalent and has one valence electron
in excess compared to silicon. A boron-doped p-type silicon crystal has, therefore,
more free holes (it is p-type, e.g. “positive”), in contrast with a phosphorous-doped
silicon crystal, which provides more free electrons (it is n-type, e.g. “negative”). A
traditional solar cell consists of a p-region bordering on an n-region. Through charge
exchange, one obtains, at the interface of the two regions, a pn-junction. which is
associated with the following effects:
(a) Diffusion of phosphorous
In the traditional process of crystal growing for solar cells, the silicon base material
is doped with boron (to become p-type silicon) and ingots are grown. From these
S. Leu and D. Sontag
therefore these topics fit better into the chapter on Heterojunction (HJT) cells. For
these reasons, this chapter does not deal with cleaning and texturization.
5.2 Cell Processing for the Al-BSF Cell
This section describes the basic steps for manufacturing a solar cell. We describe
first of all the Al-BSF (Aluminium Back Surface Field) cell, which was the most
widely used solar cell until 2015. It was then further developed and led to the PERC
cell, which is described in Sect. 5.3.
5.2.1 Light Trapping by Texturization
The first step in cell production is the Texturization. To get a high efficiency, we
increase the front side of the cleaned, microcrack free and saw damage free wafer surface. We increase the surface area by texturing the wafer. We have already described
this in Chap. 4.
5.2.2 Formation of the pn-Junction
The presence of a charge-separating pn-junction is a prerequisite for a functioning
traditional Al-BSF solar cell. In crystalline solar cells, one employs silicon as a
semiconductor material—with boron and phosphorus as dopants. Silicon is tetravalent, so it has four valence electrons, through which a bond to neighbouring atoms
can be implemented. Boron is trivalent and has, thus, one valence electron missing
compared to silicon, while phosphorus is pentavalent and has one valence electron
in excess compared to silicon. A boron-doped p-type silicon crystal has, therefore,
more free holes (it is p-type, e.g. “positive”), in contrast with a phosphorous-doped
silicon crystal, which provides more free electrons (it is n-type, e.g. “negative”). A
traditional solar cell consists of a p-region bordering on an n-region. Through charge
exchange, one obtains, at the interface of the two regions, a pn-junction. which is
associated with the following effects:
(a) Diffusion of phosphorous
In the traditional process of crystal growing for solar cells, the silicon base material
is doped with boron (to become p-type silicon) and ingots are grown. From these