Topcon

TOPCon, short for Tunnel Oxide Passivated Contact, is a solar cell architecture that uses a thin silicon oxide layer and a heavily doped polysilicon contact to form a passivated, low-resistance electrical contact. In a TOPCon cell, a native or deliberately grown very thin oxide layer (approximately 1–2 nm) is created on the silicon wafer surface. A layer of doped polysilicon, typically phosphorus-doped for n-type contacts, is deposited on the oxide. The oxide acts as a tunnel barrier that reduces surface recombination, while the doped polysilicon provides a conductive contact for carriers to reach the metal grids. The resulting contact is highly passivated and enables low contact resistance due to the high dopant concentration in the polysilicon, while avoiding metal-induced recombination that plagues conventional contacts.

TOPCon can be implemented on either the front or back side, but most commercial implementations focus on back-side passivated contacts (back TOPCon) to combine with existing wafer-based device structures, such as PERC. There are n-TOPCon and p-TOPCon variants, depending on the type of dopant in the polysilicon layer.

Compared with other passivated-contact approaches such as Heterojunction with intrinsic thin layer (HJT), TOPCon aims to deliver high open-circuit voltages with a potentially simpler manufacturing sequence and lower material costs, at the expense of added process steps for oxide formation and polysilicon deposition. Research continues to optimize oxide thickness, dopant activation, and interface quality to minimize recombination and series resistance.

Commercial activity has grown since the 2010s, with several manufacturers offering TOPCon-compatible cells and modules alongside other passivated-contact technologies.