Fig 6. (a) SEM image of the Ag/Cu bi layer stack contacts after
contact co-firing, the metals detached from each other created high line
resistance and (b) SEM image of the Ag/Ni contact lifts off
from the Si substrate
The efficiency and series resistance parameters, plotted based on finger
width associated with lift-off and delamination in stacked contacts, are
presented in Fig. 7. The results show that bi-layer contacts perform
similarly to Ag counterparts, provide no delamination or a lift-off
occur in the structure. Lift-off from the center damages the performance
to the extent that the efficiency of Ag/Ni contacted cell may drop to as
low as 16.62% as shown by the highlighted datapoints in Fig. 7 (left).
The series resistance of those cells, shown in Fig 7 (right), may exceed
1Ω·cm2 due to high contact resistance while
delamination present itself as a finger resistance and increases the
RS for the Ag/Cu contacts. For those cells where the
contact layers are intact, the contact resistance is in the range of the
Ag reference, implying that the performance can reach industry standards
and lower the Ag usage per watt. Following this data, it can be
concluded that the performance of both Ag/Cu and Ag/Ni contacts closely
mirrors that of their Ag counterparts. These findings suggest a high
potential for these bi-layer configurations to serve as effective
alternatives to Ag, especially considering their performance, which is
commensurate with industry standards. By leveraging these alternatives,
a considerable reduction in Ag consumption per watt can be achieved
without compromising the efficiency of solar cells.