What is TOPCon?
TOPCon is Tunnel Oxide Passivated Contact in short name. Its essence is a special oxide layer like a tunnel, which is made of ultrathin silicon oxide.
Where is it?
Its location is as the picture shown below, between the bottom side of silicon bulk and poly silicon layer. It acts as surface passivation layer, and needs to be thin enough so that current can tunnel through it quantum mechanically.
Therefore, it is like a tunnel. That’s how TOPCon got its name.
What is the purpose of it?
We mentioned in the PERC Solar Panel article that electrons recombine easily with silicon atoms. In order to reduce the recombination of electrons and silicon atoms (or called suppress recombination), and increase the current, a passivation layer and rear contacts are required.
TOPCon technology actually merge a thin film in the passivated contact structure, restraining recombination and increasing charge-carrier selectivity, so also means Selective Passivation Contact. This technical feature can further reduces resistance loss and increase voltage.
This structure is big difference from P-PERC, you can learn more about it in N-type and P-type solar cells.