A analysis crew from the College of New South Wales (UNSW) investigated the failure modes of heterojunction (HJT) photo voltaic modules with glass-backsheet configurations.
“We recognized 4 failure modes within the silicon heterojunction glass-backsheet module which have the potential to end in energy lack of as much as 50% after damp warmth testing,” stated researcher Chandany Sen. pv journal. “We purpose to know the potential root trigger of every failure mode and the right way to detect it simply on the cell degree.”
The scientists carried out their experiment on bifacial half-cut n-type silicon HJT photo voltaic cells that got here from industrial manufacturing traces of unknown producers. The merchandise are divided into three teams: modules with encapsulated cells; modules with encapsulated cell precursors; and non-encapsulated cells. For the primary two teams, the researchers used ethylene vinyl acetate (EVA) encapsulant.
“All samples have an n-type wafer, intrinsic hydrogenated amorphous silicon (ia-Si:H) passivation layers on each side, and phosphorus-doped (na-Si:H) and boron-doped (pa -Si:H) hydrogenated amorphous silicon layers on the back and front sides, one after the opposite, adopted by an indium-doped tin oxide (ITO) layer deposited on each side,” they stated.
All gadgets are subjected to a moist warmth check at 85°C and 85% relative humidity (RH) for a period between 500 hours and 4000 hours.
By means of this check, the teachers recognized 4 failure modes for the encapsulated cells, leading to energy loss from 5% to 50%. The primary sort of failure consists of cell darkening in localized factors, and the second is represented by darkening across the interconnection of busbars and ribbon wires. The third failure mode includes extreme darkening between the connecting areas of the busbars and ribbon wires, whereas the fourth exhibits the darkening of the interconnected area of the busbars and ribbon wires.
Based on the group’s evaluation, the primary sort of failure is because of floor contamination, which can have occurred throughout dealing with or identification earlier than the encapsulation of the module. As for the second and third teams, scientists say that the failures are associated to the soldering flux.
“The direct impact of flux and lead (Pb) solder on inflicting contact deterioration after DH testing has additionally been noticed in different works,” they stated. “It must be emphasised that, in some instances, using a unique Ag paste additionally resulted in a Kind-3 failure.”
For the fourth group, the researchers confirmed that the failures in all probability got here from the byproduct of the EVA used for encapsulation.
“Though the experimental design of this work can not decide precisely how every failure mode occurred after the DH check, it exhibits believable conditions that may happen within the industrial setting and result in precise modes of failure noticed,” they concluded.
Sen stated that understanding and mitigating these failure modes, ideally on the photo voltaic cell degree, can be essential to realizing the low value of electrical energy (LCOE) potential of the HJT. He stated that whereas glass-glass modules are sometimes used for HJT photo voltaic cells due to their decreased susceptibility to moisture ingress, comparable failure modes are inclined to happen in these modules over longer durations of time.
The analysis crew offered its findings within the examine “4 failure modes of silicon heterojunction glass-backsheet modules,” printed in Photo voltaic Power Supplies and Photo voltaic Cells.
