pTOPCon

pTOPCon, short for p-type Tunnel Oxide Passivated Contact, is a back-contact passivated solar cell architecture. It uses a thin tunnel oxide on silicon and a heavily doped p-type polycrystalline silicon layer to form a low-resistance, passivated back contact on crystalline silicon wafers.

The typical structure places a 1-2 nanometer silicon oxide layer on the rear surface of a silicon wafer, followed by a p+-doped poly-Si layer, deposited by PECVD or sputtering. A metal grid is deposited on the poly-Si to form the rear electrical contact. The oxide reduces surface recombination, while the heavily doped poly-Si supplies conductivity through tunneling.

Fabrication involves oxide growth, deposition and activation of the p+-Si contact, and rear contact metallization; post-deposition anneals improve dopant activation and interface passivation.

Performance advantages include reduced recombination at the rear, potential increases in open-circuit voltage and overall efficiency, compatibility with existing back-contact solar cell processes, and lower parasitic absorption compared with some alternative contacts. Challenges include precise control of oxide thickness, dopant activation uniformity, and long-term stability under device operating conditions.

P-type TOPCon is one of several TOPCon variants, alongside n-TOPCon, differing primarily in the dopant type of the poly-Si contact and the doping of the silicon wafer. It is part of ongoing research to improve rear passivation and allow high-efficiency, scalable manufacturing for commercial solar cells.