From pv magazine Global
A research team from the University of New South Wales (UNSW) has investigated failure modes in heterojunction (HJT) solar modules with glass-backsheet configurations.
“We have identified four failure modes in the silicon heterojunction glass-backsheet module which has the potential to result in a power loss of up to 50% following damp heat testing,” researcher Chandany Sen told pv magazine. “We sought to understand the possible underlying causes of each failure mode and how to quickly detect them at the cell level.”
The scientists conducted their experiment on bifacial half-cut n-type silicon HJT solar cells sourced from industrial production lines of unidentified manufacturers. The products were divided into three groups: modules with encapsulated cells; modules with encapsulated cell precursors; and non-encapsulated cells. For the first two groups, the researchers used ethylene vinyl acetate (EVA) encapsulant.
“All samples featured an n-type wafer, intrinsic hydrogenated amorphous silicon (i-a-Si:H) passivation layers on both sides, and phosphorus-doped (n-a-Si:H) and boron-doped (p-a-Si:H) hydrogenated amorphous silicon layers on the front and rear sides, respectively, followed by indium-doped tin oxide (ITO) layer deposited on both sides,” they said.
All devices underwent a damp heat test at 85°C and 85% relative humidity (RH) for durations between 500 hours and 4000 hours.
Through this testing, the academics identified four failure modes for the encapsulated cells, resulting in power losses ranging from 5% to 50%. The first failure type consisted of cell darkening in localized points, and the second was represented by darkening around the interconnection of busbars and ribbon wires. The third failure mode involved intense darkening between the interconnected regions of busbars and ribbon wires, while the fourth showed darkening on the interconnected region of busbars and ribbon wires.
According to the group’s analysis, the first failure type was attributable to surface contamination, which may have occurred during handling or characterization before module encapsulation. As for the second and third groups, the scientists attributed the failures to the involvement of soldering flux.
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