Electrical Signatures of Contact Degradation for c-Si Solar Cells
Reza Asadpour, Xingshu Sun, Muhammad A. Alam
Purdue University, West Lafayette, IN, United States

There is a vast literature on the reliability of solar cells that empirically correlates the stress factors (e.g. moisture, voltage) to degradation mechanisms (e.g. corrosion, PID) to module electrical signatures (e.g. series/shunt resistances). In this paper, we use the illustrative example of moisture- and stress-induced contact degradation to show that the perceived empirical correlations can be misleading, if not completely wrong. By interpreting the spatially-resolved voltage-maps and terminal I-V characteristics obtained from cell simulator Griddler, we positively correlate the series resistance increase to the broken tabbing points. Remarkably, however, it is easy to misattribute finger corrosion to PID because it appears as a fake shunt in the terminal I-V characteristics.  The underlying physical principle suggests two new characterization techniques to distinguish real vs. fake shunts. Our novel use of cell simulator opens up a new avenue for predictive reliability modeling of solar cells.