A group of researchers led by the Chinese Academy of Sciences claims to have improved silver paste quality for producing solar cells based on tunnel oxide passivated contact (TOPCon) solar cells via the so-called laser-enhanced contact optimization (LECO) process.
The process is carried out after the firing of the metallization paste and involves scanning a laser across a crystalline silicon cell while it is under reverse bias. The result is that free carrier electrons are forced between the metal contact and the silicon, creating a new structure on the edge of the contact and boron emitter layer surface – a current-fired contact (CFC). By virtue of the new CFC structure, TOPCon cells that undergo the LECO process demonstrate no contact resistivity after thermal cycling.
“An urgent improvement in LECO-compatible silver pastes is required to ensure the reliability and stability of TOPCon solar cells,” the research's corresponding author, Jiangtao Di, told pv magazine. “Herein, we studied optimizing glass formation by introducing elements such as aluminum, gallium, and iron into the inorganic glass frits of conductive silver pastes.”
The research group created new types of LECO silver pastes integrating aluminum (Al), gallium (Ga) and iron (Fe) in the glass frits, respectively, with the aim of evaluating their acid corrosion stability through the acetic acid degradation test.
“We examined the degradation of TOPCon solar cells under standard acetic acid conditions,” Di explained. “The silver paste crafted with glass frits containing added Al, Ga, or Fe elements exhibited significantly enhanced resistance to acetic acid corrosion compared to silver paste lacking these special elements.”
The analysis showed that the new glass frits ensured that cells' electrodes remained securely anchored to the silicon cell surface due to the enhanced stability of the lead oxide (PbO) component in the glass powder.
“The efficiency loss of LECO-used silver paste with Al/Ga/Fe additives during acetic acid exposure can be less than 10%, and even as low as 5%,” Di went on to say. “In contrast, without the introduction of these special elements, the degradation effect of acetic acid can markedly increase to over 50%.”
“Our work offers highly reliable LECO-compatible silver pastes for TOPCon solar cells,” he concluded.
The research's findings are available in the study “Strengthening TOPCon solar cell reliability via Al/Ga/Fe-added glass frits in LECO-compatible silver pastes against acid corrosion,” which was recently published in Solar Energy Materials and Solar Cells.
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