Researchers from UNSW and Longi have discovered that the silicon nitride layers used in the rear of the top concel are particularly susceptible to chemical demolition of sodium contamination. This can lead to significant open-circuit voltage losses and reducing cell efficiency.
A research team from the University of New South Wales (UNSW) and Chinese solar module maker Longi has investigated the demolition of topcon sun cells under exposure to the damp heating and has discovered that the silicon nitride (sin (sin (sinX ) Low at the rear of the cell is particularly vulnerable to chemical demolition of sodium (post) contaminants.
“This subject has not received much attention to the date, but serious care is now that the stability of front metallization has improved,” said the corresponding author of the research, Bram Hoex, said PV -Magazine.
In the newspaper “The mitigating by polluting induced surface breakdown in topcon sun cells: mechanisms, effects and mitigation“Which was recently published in Solar energy materials and solar cellsHoex and his colleagues explained that Sinx-vulnerability at the rear can lead to SIgaillante losses of open-circuit voltage, substantial resistance increase and total degradation of cell performance.
The researchers used various after-related salts to examine the demolition of open circuit voltage in topcon sun cells under cell level moisture heat (DH) tests. The DH test is an accelerated test that test the reliability of modules under extreme humidity and heat. In its standard shape, the PV is placed in a controlled room with a temperature of 85 ° C and humidity of 85% for at least 1,000 hours.
The tests were carried out on commercial species of 23%-efficient topcon cells. At the front, the devices contain a drill-different emitter, passivated by a multi-layered stack of aluminum oxide (ALOX), a sinX Low and a silicon oxynitride (SIOyNZ) Low as an anti -reflection coating (ARC).
At the back, the cells had a tunneling silicon oxide (SIO2) Low, a phosphorus-merged polycrystalline silicon (poly-si) low and an extra sinX Arch layer. In addition, the front was treated with Silver (AG) and aluminum (Al), while the rear contact was formed using a screen-printed AG pasta.
Image: Unsw, Solar Energy Materials and Solar Cells, CC by 4.0
The HD tests were performed for 20 hours in an ASLI environment room with 85 ° C with 85% relative humidity (DH85). It showed that in particular two sodium contamination – CH3Coona and Sodium chloride (NaCl) – were responsible for important performance losses.
“In our experiments, the application of CH is3Coona at the back of the Topcon cells led to a considerable loss of 16% in efficiency, while NaCl caused a relative decrease of 4.8%, “the academics said. ‘The sin backX Low was particularly sensitive to chemical reactions and breakdown on the surface when exposing on sodium-based salts, resulting in increased oxidation, passiveness loss and a clear reduction of the most important performance parameters, such as open-circuit voltage, with severe filling factor (FF) degradation when treated with che treated with treated3Coona. “
The analysis also showed that open-circuit voltage losses can reach up to 5.8%, with a relative loss of total cell efficiency around 16%.
The research group suggested tackling the analyzed degradation mechanisms by iIn the cell rontant, a barrier layer of 10 Nm aluminum oxide (Alox), deposited via atomic layer deposit (ALD), to protect against polluting diffusion.
“This layer effectively reduced the breakdown of performance, which only demonstrates a small decrease in efficiency and retaining the stability of the open circuit voltage after 20 hours of accelerated moist tests of the damp heating,” explained it further. “The ALOX Low also mitigates corrosion and recombination defects induced by sodium-related salts, so that its potential is confirmed as a robust protective solution to improve the long-term reliability of topcon sun cells under hard environmental conditions. “
“Accelerated moist tests confirmed that the Alox layer significantly reduces the breakdown, so that the long-term stability maintains,” Hoex added. “Our solution represents asCalermeable and industrially feasible approach for improving the reliability of the Topcon sun cells. “
Looking ahead, the academics said they want to better integrate barrier layers in commercial production and want to analyze long -term degradation behavior under real field conditions.
Earlier research by UNSW showed the vulnerability of Topcon sun cells to contact corrosion and three types of Topcon zone module errors that were never detected in perc panels.
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