What is a TOPCON solar cell?

TOPCON (also known as passivated contact) solar cell, is touted as the next generation of solar cell technology after PERC. This novel architecture is introduced by researchers at Fraunhofer Institute for Solar Energy Systems in Germany in 2013 [1].

Compared to the other potential new technologies, such as HJT and IBC, TOPCON can be upgraded from the current PERC or PERT line. As a result, lower capital investment is needed for existing PERC or PERT manufacturers who are looking to upgrade their existing production lines. Moreover, a good gain in solar cell efficiency can also be achieved. This is ~1% in absolute value as reported in [1].

TOPCON is the acronym for “Tunnel Oxide Passivated Contact”. Figure 1 show this cell architecture as compared to a n-PERT solar cell.

Figure 1. n-PERT compared to n-TOPCON solar cell architectures

As shown in the figure, n-PERT and n-TOPCON are quite similar. Typically, to upgrade an n-PERT solar cell to a n-TOPCON solar cell, only an additional ultra thin SiO2 layer and a doped poly-Si layer are required.

The ultrathin SiO2 acts as surface passivation layer between the rear Si surface and the rear “contact” – the poly-Si layer. In addition, it also needs to be thin enough so that current can tunnel through it quantum mechanically.

The poly-Si layer is highly doped to produce a high conductivity layer. This high conductivity layer will then acts as a contact for current collection. Additionally, in a n-type TOPCON, the poly-Si layer is typically doped with phosphorus to provide field passivation (back surface field). This is similar to the phosphorus doped rear surface of n-PERT as shown in figure 1(a).

With the addition of the tunnel oxide layer, the original authors at Fraunhofer Institute for Solar Energy Systems reported an increase of ~1% in absolute solar cell efficiency [1] [2].