Fig. 2 Top view SEM images of the two bi-layer stack contacts
after firing
Supporting the above-mentioned premise, the results of finger resistance
(RF) for the single layer Ni contact compared to the
single layer Ag contact across different firing profiles, as depicted in
Fig. 3a, demonstrate promising outcomes. Particularly, screen-printed Ni
contacts at the industry-standard peak temperature of around 770-800°C
(on the sample) exhibit favorable results in finger resistance compared
to Ag counterparts. The RF shows limited deviation with
varying contact co-firing peak temperature, suggesting that metal
particle sintering occurs properly for both Ni and Ag contacts This can
potentially be attributed to softening of Ni metals at the intersection
of Ni/Si predominantly occur at elevated temperatures. Comparing the
contact resistance of two single layer contacts, on the other hand,
proves that Ag makes a better contact with Si than Ni as seen in Fig.
3b. This advantage stems from Ag’s lower metal work function compared to
Ni. The closer alignment of Ag’s work function with Si’s electron
affinity (~4.05 eV) facilitates efficient charge carrier
transfer across the metal-semiconductor interface, thereby reducing
contact resistivity. Additionally, the relatively low contact resistance
observed for both contact types suggests that the in-house prepared
glass frit is effectively etching the ARC layer without damaging the
emitter. This is further supported with power conversion efficiency and
fill factor (FF) results of both single layer contacts, as shown in
Figure 4. In line with the result of resistivity measurements of the
contacts, the FF and the efficiency for Ni contacts suffer due to high
series resistance thereby underscoring the potential of Ag as a viable
seed layer.