What is a PERC solar cell?
Passivated rear emitter contact solar cell, or PERC in short, is a new type of solar cell architecture that has caught the solar PV industry by storm. Invented by a group headed by Prof. Martin Green in UNSW in the 80s & 90s, this technology has been deployed by most of major solar PV manufacturers in the world as in 2019.
Figure 1 shows a traditional Si solar cell architecture that has accounted for most of the solar PV cells manufactured in the world in the early and mid 2010s. The solar cell is based on p-type Si wafer. The front surface (emitter) is passivated by dielectrics such as SiNx, which also act as an antireflection layer. The rear surface of the Si wafer, however, is not passivated by any dielectric. Aluminium (Al) is being doped into Si to form a back surface field (BSF) during metal co-firing process to act as a high-low junction that prevent minority carriers from recombining at the rear surface.
On the other hand, for a PERC solar cell as shown in Figure 2, both the front and rear surfaces of the device are passivated by dielectrics. Small pockets of the rear dielectric layer are opened (etched away) with laser so that metal can be contacted to the rear surface of the device.
Compared to a conventional Si solar cells, PERC is able to improve the efficiency of Si solar cells mainly due to the additional passivating dielectric layer on the rear side, through:
1. Rear side passivation that prevent minority carriers (current generated from light absorption) from recombining (eliminated) at the rear surface.
2. The extra rear dielectric layer reflects long wavelength photons from the rear surface back to the device for more light absorption and current generation.