TOPCon vs PERC – a battle between steep learning curves – pv magazine International
TOPCon solar modules will gain more market share if their average efficiency, already higher than that of PERC panels, continues to improve, according to Stefan Glunz, head of PV research at Germany’s Fraunhofer Institute for Power Systems. solar ISE. In an upcoming pv magazine webinar on the potential of TOPCon technology, Glunz will show how to reduce costs and increase efficiency.
Excerpt from pv magazine Global
TOPCon photovoltaic technology is constantly gaining new market share in all segments and is the strongest candidate to challenge the primacy of PERC solar panels. However, success will depend on several variables that are still difficult to decipher.
“TOPCon PV technology has a very high yield potential, already reaching 26% in research, which explains its current adoption,” said Stefan Gunz, head of the photovoltaic – research division at Germany’s Fraunhofer Institute for Systems. solar energy ISE. photo magazine. “However, PERC panel technology also has a very steep learning curve and the balance between them will depend on which one is able to increase efficiency or reduce costs faster than the other.”
He said TOPCon products will have more opportunities to gain traction in the race if their average efficiency, which is already comparatively higher than PERC products, is further increased.
“TOPCon manufacturers still have room to cut costs, especially when it comes to intrinsic/doped polysilicon deposition,” he said. “But the real step forward can be taken by further increasing their efficiency, which would ensure that the possibly slightly higher costs involved in producing TOPCon will be more than justified, as TOPCon panels have higher efficiency and energy efficiency. .”
However, it is still unclear to what extent their effectiveness should be increased.
“The manufacturers are not very transparent about their current achievements,” the German scientists said. “And it doesn’t make it easy to understand which new TOPCon panels can really resemble PERC products in terms of a good trade-off between cost and performance.”
The future also remains difficult to predict.
“As always, predicting TOPCon’s market share is a peek into the crystal bowl, but since PERC, as the dominant cellular technology, has a large technological overlap with the TOPCon route, the change may be quite smooth and similar to the transition of aluminum from back surface field solar cells (Al-BSF) to PERC devices,” Glunz said.
Glunz and other scientists from Fraunhofer ISE and the University of Freiburg in Germany described the trajectory of TOPCon technology in “Silicon-based passivating contacts: The TOPCon route”, which was recently published in Progress in photovoltaics.
The study dates back to the 1980s, when the first attempts to use polysilicon layers under the contacts to reduce recombination in silicon solar cells were published.
“No details of the manufacturing process for these passivating contacts have been released. Given SunPower’s respective expertise demonstrated by their patent portfolio, it seems likely that poly-Si/SiOX contacts were used,” the newspaper read.
The first TOPCon cell, for which the use of poly-Si-SiOX contacts was officially unveiled, is a 23% efficient device, with a high open circuit voltage of 698mV, built by Frank Feldmann of ISE Fraunhofer in 2013. It was a double-sided contacted device that was very similar to the current industrial cellular structures.
“The recombination properties of early n-type TOPCon cells were limited primarily by recombination at the forward contacts,” the researchers explained, noting that the technology has experienced a renaissance over the past decade. “In fact, the introduction of a local p++ boron diffusion under the front contacts and other improvements led to a record efficiency of 25.8% (Vof oc = 724 mV) on not-TOPCon type cells.
Glunz also noted that a recent TOPCon cell structure featuring a rear junction on p-type silicon even resulted in 26% efficiency, with an open circuit voltage of 732 mV.
The research group has identified four research topics that are currently being addressed to improve the technology: the need to reparameterize intrinsic recombination in silicon due to the excellent surface passivation of TOPCon structures; improve the control of dopant diffusion through the SiO intermediateXlayer to optimize passivation and transport properties; unilateral deposition of the poly-Si layer to reduce process complexity for industrial TOPCon cells; and the use of silicon-based tunnel junctions in perovskite-silicon tandem cells based on a TOPCon design.
“In particular, the unilateral deposition of the poly Si layers, or the corresponding unilateral etching in the case of bilateral deposition, as well as a lightened metallization route for TOPCon cells are currently of great importance for the industrial introduction of TOPCon. “, says Glunz.
He added that TOPCon PV technology will possibly co-exist with PERC and heterojunction modules within the current decade.
“Since TOPCon and PERC cells share many process steps, we could see quite a large market share of this TOPCon in the future,” he said.
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