German researchers have assessed recent studies into hydrogen -related breakdown in silicon solar cells. They said that the work is at the right time, with the silicon of the N-type that dominates production and emerging antimony doping.
Hydrogen can be beneficial for silicon zonnet technologies, bulk and surface defects passivate, or harmful, which contributes to degradation (Letid) and surface-related breakdown (SRD) induced by light and increased temperature.
In order to promote a better understanding of recent research results on the use of hydrogen with silicon (SI) solar cells and the related degradation symptoms, researchers from Fraunhofer Institute for Solar Energy Systems (Fraunhofer Isee) and the University of Freiburg have assessed the literature and discussed their findings. They then published “Review on hydrogen in silicon solar cells: from its origin to its harmful effects“In Solar energy and materials.
“In recent years we have seen intensive research into hydrogen in silicon solar cells from multiple institutions. The review paper provides an overview of these results, aimed at the introduction of hydrogen in silicon solar cells and the relationship between hydrogen and breakdown fens,” said researcher Benjamin Hammann said PV -Magazine. “In general, hydrogen has always been an important topic for silicon solar cells because of the ability to passivate defects, both in the bulk and on the surface. With N-type SI dominating solar cell production and antimony (SB) Doping, new questions about hydrogen also arise.”
The researchers have considered more than 170 publications and books on the subject, “although they were not all relevant to the assessment,” said Hammann. Ultimately, the Review 77 references, with regard to research into the use of hydrogen with P-Type silicon, drill-doped float-zone (FZ) silicon and gallium-doped Czochralski (CZ) grown silicon and including Passivated emitter) and tunnel-tunnel) (Topconcon) technologies.
“Insight into the introduction of hydrogen in silicon solar cells, together with its negative impact, helps the manufacturers of solar cells to assess the result of process adjustments,” Hammann explained. He further noticed that Topcon sun cells, for example, need hydrogen for excellent surface passion, “while the silicon of the N-type is still susceptible to degradation of light and raised temperature (Letid), albeit less than P-type.”
Disadvrich that much “remains unknown” about hydrogen in silicon of the N-type, Hammann said that the review “serves as a good starting point for research into hydrogen in silicon of the N-type, because extrapolating results from one doping type to the other can offer a first hypothesis.”
One of the first findings was that Letid ‘is limited if the total hydrogen concentrations are lower than 5 x 1014 cm-3. “
The team found a similar limit of the upper tolerance limit for an aluminum oxide/silicon nitride passivating layer stack. The research team then discussed various strategies to control the hydrogen content.
“An important factor is the hydrogen source, typically hydrogen -rich silicon nitride,” they noticed. It was also marked that the hydrogen diffusion process takes place “mainly during the fast step, including both in-diffusion around peak temperature and out of diffusion during the subsequent cooling.”
The effects of “other intermediate layers”, such as aluminum oxide or highly doped surface-needle layers, on the diffusion process were also discussed.
To the question of the findings with regard to SRD, Hammann said that many passivities, such as aluminum oxide, silicon nitride and even topcon layers are influenced by a form of SRD.
“It is very likely that SRD is connected to hydrogen, although there are still many questions about answering, of which we are currently conducting an investigation,” he said.
The research team is now investigating SRD from topcon layers and is investigating UV-induced demolition of topcon sun cells.
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