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.