# Research Progress of Zero-Busbar Technology Based on Heterojunction Photovoltaic Modules
## 3 Results and Analysis
### Reliability Analysis
#### 3.2.2 Metal Paste Selection
Figure 12: EL images of soldering-based 0 BB modules: (**a**) initially with Ag@Cu paste, (**b**) after TC200 with Ag@Cu paste, (**c**) initially with silver paste, and (**d**) after TC200 with silver paste. (**e**) The retention rates of the silver and Ag@Cu pastes after the solderability test. Furthermore, the modules using the two pastes were tested after the HF20 test, and the results are shown in Table 3 and Figure 13. The module using the Ag@Cu paste shows a problem similar to that above of initial EL defects (Figure 13a), and similar behaviors of de-soldering and the breakage of fingers in the SRCAs are shown in Figure 13b, with a decrease in FF and a 4.79% drop in module power after the HF20 test. The module using the silver paste still shows high stability after the HF20 test, with no visible defects in the EL images (Figure 13c,d) and a negligible amount of power loss. For the IFC-based 0 BB modules, the same silver and Ag@Cu pastes were chosen, using the optimized Bi26 solder. TC200 tests were performed on two types of modules, and the results are shown in Table 4 and Figure 14. Compared with the initial EL (Figure 14a), the module with sliver paste fingers has minor detaching (which is similar to the red area in Figure 14b); thus, the fill factor shows a minor decrease. The module with Ag@Cu fingers shows no significant defects in the EL image after the TC200 test (Figure 14c,d), and the module's \(V_{ox}\), \(I_{sc}\), \(FF\), and \(P_{max}\) values barely change. Furthermore, the IFC-based 0 BB modules using both finger pastes were subjected to the DH1000 test, and the results are shown in Table 5 and Figure 15. The module with silver paste fingers shows no significant difference in the EL images (Figure 15a,b), and only slight darkening at the bottom-right corner of the EL image (Figure 15b) is observed due to the moisture ingress. Its power decreases by 2.11%. The module with Ag@Cu paste fingers \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type** & \(\Delta V_{ox}\)/\% & \(\Delta I_{sc}\)/\% & \(\Delta FF\)/\% & \(\Delta P_{max}\)/\% \\ \hline Silver & 0.30 & 0.02 & \(-\)0.98 & \(-\)0.63 \\ Ag@Cu & 0.16 & \(-\)0.13 & 0.14 & \(-\)0.09 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Electrical parameters of IFC-based modules after TC200. Figure 13: EL images of soldering-based 0 BB modules: (**a**) initially with Ag@Cu paste, (**b**) after HF20 with Ag@Cu paste, (**c**) initially with silver paste, and (**d**) after HF20 with sliver paste. shows no significant difference in the EL images (Figure 15c,d), and its power decreases by 2.22%. Considering the acceptable TC200 and DH1000 test results, as well as the lower silver consumption, the Ag@Cu paste is a better choice for the IFC-based 0 BB design. Figure 14: EL images of IFC-based 0 BB modules: (**a**) initially with silver paste, (**b**) after TC200 with silver paste, (**c**) initially with Ag@Cu paste, and (**d**) after TC200 with Ag@Cu paste. Figure 15: EL images of IFC-based 0 BB modules: (**a**) initially with silver paste, (**b**) after DH1000 with silver paste, (**c**) initially with Ag@Cu paste, and (**d**) after DH1000 with Ag@Cu paste. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type** & \(\Delta\mathbf{V}_{ac}\)/\% & \(\Delta\mathbf{I}_{sc}\)/\% & \(\Delta\mathbf{FF}\)/\% & \(\Delta\mathbf{P}_{max}\)/\% \\ \hline Silver & \(-0.08\) & \(-0.31\) & \(-1.72\) & \(-2.11\) \\ Ag@Cu & \(0.06\) & \(-1.10\) & \(-1.23\) & \(-2.22\) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Electrical parameters of lamination-based modules after DH1000.