Researchers in South Korea have discovered that the contamination by small amounts of soldering clux residues during the production of heterojunction PV module production can cause considerable long-term relegation. Careful control of Flux -Collection Methods and the recording of drying steps are presented as potential solutions.
A group of researchers from the Korea Electronics Technology Institute (Keti) has investigated how commercially available soldering fluxes IndiumTin oxide (ITO) electrodes in hetero junction (HJT) can corrode solar cells and have discovered that there is a significant risk of early breakdown trial.
Solder fluxes are used to remove the oxide from the tab ribbons or bus ribbons during the module assembly process.
The scientists in particular analyzed four on the market available fluxes – 920, 952, 56 and 180 – under harsh conditions, including high humidity and temperature. “The fluxes were dried in advance, which resulted in a highly concentrated, thick pasta-like consistency,” they explained. “Solder flux was deliberately dropped on the front and rear ito layers during the tab process.”
The flux residues were removed via sonication after relegation of moisture heat (DH) for 45 hours. However, a series of electroluminescence (EL) images showed that the residues were not completely removed, which caused the formation of dark spots on the cells.
Through other experiments, the research team discovered that placing soldering flux on the ITO layer of HJT cells leads to “serious” loss of electrical conductivity.
“This corrosion behavior is particularly pronounced on the ITO layer back due to the clear structural difference in comparison with the ITO layer front, in particular a higher tin (SN) content that results in tinoxide (SNO2) Phasegregation confirmed in X -ray fraction (XRD) analysis, “it said.” X-ray photo-emission spectroscopy (XPS) measurements also indicate a relatively high concentration of oxygen vacancies on the back ITO layer. “
The scientists also discovered that Flux 920 showed the highest breakdown speed for both sides of the ITO layers, because of the highest acidity, with the fluxes 180, 952 and 56, which have a similar acidity that showed a lower breakdown speed.
“In general, these findings emphasize that contamination due to small amounts of flux residues during the production of PV modules can cause considerable relegation in the long term,” concluded the academics, and noted that their work presents a method for flux application and the drying process that such breakdown problems can dissolve.
“The samples that the flux is dried and blown up before tab bearing shows almost no breakdown, which indicates that the drying and bladder process reduce the landing of solder flux on the ITO layer and therefore limit the increase in series resistance,” they added.
Their findings can be found in the study “Solder flux causes corrosion of IndiumTin -oxide -electrode in heterojunction solar cells“Which was recently published in Cell reports physical science.
In February, researchers of the University of New South Wales (Unsw) and the Chinese Canadian PV modulemaker Canadian solar Sonne-Solar investigated the effect of soldering flux on both Topcon and Heterojunction (HJT) solar cells and have determined that the choice of this component is the key to avoid potential module errors.
Through this work, the scientists discovered that power losses in the HJT cells were caused by holes in the metallization layer, which facilitates the penetration of the solder clux, leading to chemical reactions that break down the performance. Moreover, this study has also established that the ITO layer in HJT cells is very susceptible to damage caused by solder flux.
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