12.5.1
1.
2.
3.
The PERL concept
The first high efficiency concept was developed in the late 1980s and the early 1990s at
the University of New South Wales in the group led by Martin Green. Figure 12.15 shows
an illustration of the PERL concept, which uses a p-type float zone silicon wafer. With this
concept, conversion efficiencies of 25% were achieved [47]. The abbreviation PERL
stands for Passivated Emitter Rear Locally diffused. This abbreviation indicates two
important concepts that have been integrated into this technology: first, the optical losses
of the PERL solar cell at the front side are minimized using three techniques:
The top surface of the solar cell is textured with inverted pyramid structures. This
microscopic texture allows a fraction of the reflected light to be incident on the
front surface for a second time, which enhances the total amount of light coupled
into the solar cell.
The inverted pyramid structure is covered with a double-layer anti-reflective
coating (ARC), which results in an extremely low top surface reflection. Often a
double layer coating of magnesium fluoride (MgF 2 ) and zinc sulfide (ZnS) is
used as an antireflection coating.
The contact area at the front side has to be as small as possible, to reduce the
shading losses. In the PERL concept the very thin and fine metal fingers are
processed using photolithography technology.
Figure 12.15: Illustrating the structure of a PERL solar cell.
Secondly, the emitter layer is well designed. As discussed in the previous sections,
the emitter should be highly doped underneath the contacts, which in the PERL concept is
achieved by heavily phosphorus-diffused regions. The rest of the emitter is moderately
doped, or in other words lightly diffused, to preserve an excellent blue response. The
emitter is passivated with a silicon oxide layer on top of the emitter to suppress surface
recombination as much as possible. With the PERL concept, the surface recombination
velocity could be reduced so far that open circuit voltages with values of above 700 mV
1.
2.
3.
The PERL concept
The first high efficiency concept was developed in the late 1980s and the early 1990s at
the University of New South Wales in the group led by Martin Green. Figure 12.15 shows
an illustration of the PERL concept, which uses a p-type float zone silicon wafer. With this
concept, conversion efficiencies of 25% were achieved [47]. The abbreviation PERL
stands for Passivated Emitter Rear Locally diffused. This abbreviation indicates two
important concepts that have been integrated into this technology: first, the optical losses
of the PERL solar cell at the front side are minimized using three techniques:
The top surface of the solar cell is textured with inverted pyramid structures. This
microscopic texture allows a fraction of the reflected light to be incident on the
front surface for a second time, which enhances the total amount of light coupled
into the solar cell.
The inverted pyramid structure is covered with a double-layer anti-reflective
coating (ARC), which results in an extremely low top surface reflection. Often a
double layer coating of magnesium fluoride (MgF 2 ) and zinc sulfide (ZnS) is
used as an antireflection coating.
The contact area at the front side has to be as small as possible, to reduce the
shading losses. In the PERL concept the very thin and fine metal fingers are
processed using photolithography technology.
Figure 12.15: Illustrating the structure of a PERL solar cell.
Secondly, the emitter layer is well designed. As discussed in the previous sections,
the emitter should be highly doped underneath the contacts, which in the PERL concept is
achieved by heavily phosphorus-diffused regions. The rest of the emitter is moderately
doped, or in other words lightly diffused, to preserve an excellent blue response. The
emitter is passivated with a silicon oxide layer on top of the emitter to suppress surface
recombination as much as possible. With the PERL concept, the surface recombination
velocity could be reduced so far that open circuit voltages with values of above 700 mV