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.