124
S. Leu and D. Sontag
Fig. 5.13 Schematic comparison of the two basic cell concepts: standard Al-BSF cell (left) and
PERC cell (right). It is easy to see that the PERC concept focuses exclusively on the back of
the solar cell. The Back Side Coating consists of three layers: SiO x , AlO x , SiN x . The sensitive
aluminium oxide (AlO x ) layer is protected by the silicon nitride layer (SiN x ). For PERC cells, only
two additional machine processes are needed: the coating process and the laser contact-opening
process. In the PERC process, the back side SiO x coating is optional and can also be done by
oxidation. PSG means: Phosphor-silicate Glass and is described in footnote 15. Edge isolation is
described as well in footnote 15
On special samples a reduction of the surface recombination velocity to less than
5 cm s
−1 is even possible.
For various reasons such as cost, throughput and excellence of layer quality,
the PECVD process has become established in the industrial environment, for the
deposition of the Al 2 O 3 layer. Here, trimethylaluminium (TMA) and N 2 O react in
a plasma-assisted process according to the reaction equation
24N 2 O + 2Al(CH 3 ) 3 → 24N 2 + Al 2 O 3 + 6CO 2 + 9H 2 O
(5.8)
S. Leu and D. Sontag
Fig. 5.13 Schematic comparison of the two basic cell concepts: standard Al-BSF cell (left) and
PERC cell (right). It is easy to see that the PERC concept focuses exclusively on the back of
the solar cell. The Back Side Coating consists of three layers: SiO x , AlO x , SiN x . The sensitive
aluminium oxide (AlO x ) layer is protected by the silicon nitride layer (SiN x ). For PERC cells, only
two additional machine processes are needed: the coating process and the laser contact-opening
process. In the PERC process, the back side SiO x coating is optional and can also be done by
oxidation. PSG means: Phosphor-silicate Glass and is described in footnote 15. Edge isolation is
described as well in footnote 15
On special samples a reduction of the surface recombination velocity to less than
5 cm s
−1 is even possible.
For various reasons such as cost, throughput and excellence of layer quality,
the PECVD process has become established in the industrial environment, for the
deposition of the Al 2 O 3 layer. Here, trimethylaluminium (TMA) and N 2 O react in
a plasma-assisted process according to the reaction equation
24N 2 O + 2Al(CH 3 ) 3 → 24N 2 + Al 2 O 3 + 6CO 2 + 9H 2 O
(5.8)