Assessing the potential of TOPCon solar cells architecture using industrial n-type cast-mono silicon material

Abstract

Cast-mono silicon material is interesting for its lower carbon footprint compared to Czochralski (Cz) monocrystalline silicon. However, solar cells fabricated using cast-mono (CM) silicon show lower performances. In this work, two routes to make cast-mono silicon advantageous over Cz silicon are considered. The first route is to further reduce carbon footprint of cast-mono silicon, by using Upgraded Metallurgical Grade silicon (UMG-Si) feedstock instead of Solar Grade silicon (SoG-Si) feedstock. TOPCon solar cells are fabricated using both feedstocks, and cast-mono growth technology, using industrial-type furnaces. Laboratory studies show that UMG-Si can result in efficiencies higher than solar cells made of SoG-Si when feeding the material to a CM crystallization process. But when compared to Cz, CM-UMG-Si TOPCon solar cells conversion efficiency values are still 0.5%abs lower. The second route is to take advantage of the TOPCon passivation layer (e.g., poly-Si) ability to getter metallic impurities, and thus improve the quality of cast-mono material. Several TOPCon sequences are tested and their effect on the carrier recombination properties of the device are studied. In the end, solar cells are fabricated and again, UMG-Si solar cells show better results than SoG-Si solar cells, with efficiency up to 22.65%, independently confirmed.

Keywords

• cast-mono
• sog
• umg
• topcon