168
S. Leu and D. Sontag
Fig. 7.4 Simplified cross-section of a heterojunction cell in the «back contact implementation».
On the front, no fingers shadow the cell. The electricity is taken off on the back. The pn-junction is
on the back; the n-region alternates with the p-region
Kaneka even achieved η = 26.6% cell efficiency on a 6 × 6 inch HIT cell, in which
the contacts are only on the back side (back-contact cell). «HJT-IBC (Interdigital
Back Contact)» have the highest efficiencies. This is because the losses due to the
shading of the metal fingers on the front side are completely eliminated and because
there is no parasitic absorption on the front side; in fact, there is no TCO layer and
no doped a-Si on the front side (see Fig. 7.4). Today, HJT-IBC cells are not in mass
production due to the high manufacturing costs. However, with a clever design, the
costs per peak-Watt (W p ) can be kept at the same level as with «normal» HJT cells.
Figure 7.4 gives a schematic illustration of such an HJT-IBC structure.
The best measure for the quality of the passivation is the open-circuit voltage V oc ,
which, is in a HJT cell, in general, higher than 740 mV, e.g. V oc is about 15% higher
for an HJT cell, than for conventional PERC cell, where we only obtain ~660 mV
today.
S. Leu and D. Sontag
Fig. 7.4 Simplified cross-section of a heterojunction cell in the «back contact implementation».
On the front, no fingers shadow the cell. The electricity is taken off on the back. The pn-junction is
on the back; the n-region alternates with the p-region
Kaneka even achieved η = 26.6% cell efficiency on a 6 × 6 inch HIT cell, in which
the contacts are only on the back side (back-contact cell). «HJT-IBC (Interdigital
Back Contact)» have the highest efficiencies. This is because the losses due to the
shading of the metal fingers on the front side are completely eliminated and because
there is no parasitic absorption on the front side; in fact, there is no TCO layer and
no doped a-Si on the front side (see Fig. 7.4). Today, HJT-IBC cells are not in mass
production due to the high manufacturing costs. However, with a clever design, the
costs per peak-Watt (W p ) can be kept at the same level as with «normal» HJT cells.
Figure 7.4 gives a schematic illustration of such an HJT-IBC structure.
The best measure for the quality of the passivation is the open-circuit voltage V oc ,
which, is in a HJT cell, in general, higher than 740 mV, e.g. V oc is about 15% higher
for an HJT cell, than for conventional PERC cell, where we only obtain ~660 mV
today.