TOPCon
Tunnel Oxide Passivated Contact: an n-type silicon cell whose rear uses an ultra-thin oxide and doped polysilicon layer to extract current with minimal recombination.
TOPCon was introduced by Fraunhofer ISE in 2013. The rear surface of an n-type wafer is covered by a silicon dioxide layer about 1.5 nm thick, thin enough for carriers to tunnel through, followed by heavily doped polycrystalline silicon. This passivating contact lets majority carriers pass while blocking minority carriers, cutting recombination at the metal contacts that limits PERC.
Because the process is an upgrade of PERC lines (adding LPCVD or PECVD deposition and boron diffusion), manufacturers could convert capacity quickly. TOPCon became the majority cell technology in 2024 (ITRPV 2025 edition), largely through Chinese producers.
- Mass-production cell efficiency: about 24.5–26%; modules 22–23.5%.
- Bifaciality: 75–85%, well suited to bifacial ground-mount plants.
- Temperature coefficient: about −0.29 to −0.32 %/°C.
- n-type wafers avoid boron-oxygen light-induced degradation; first-year loss typically about 1%.
Open issues include higher silver consumption than PERC and sensitivity of some module designs to moisture-driven contact corrosion in damp-heat tests. Rivals in the n-type segment are heterojunction and back-contact cells.
Related terms
All terms →- PERC (Passivated Emitter and Rear Cell)
A silicon cell design that adds a passivating dielectric layer to the rear surface, reducing recombination and reflecting light back into the cell.
- Heterojunction (HJT) solar cell
A cell that sandwiches an n-type crystalline silicon wafer between ultra-thin amorphous silicon layers, giving very high voltage and a low temperature coefficient.
- Bifacial module
A PV module that collects light on both its front and rear faces, using a transparent back sheet or glass to harvest ground-reflected and diffuse light.
- Monocrystalline silicon
Silicon grown as a single continuous crystal, usually by the Czochralski method, giving the highest-efficiency and now dominant wafer type for PV.
- Temperature coefficient
The percentage change in a PV module power, voltage or current per degree Celsius of cell temperature away from 25 °C.