What are the latest issues with TOPCon solar panels?

What’s the latest?

In a newly published paper in the journal Solar Energy Materials and Solar Cells, researchers from the University of New South Wales (UNSW) explored the role of different encapsulants in TOPCon performance. They discovered that TOPCon modules exhibit power losses of 6-16% when exposed to 2,000 hours of humid, “damp heat” stress testing, depending on the encapsulant used in the module.

Modules encapsulated with POE (polyolefin elastomer) on both sides showed the lowest degradation (around 8%) while those with EVA on the rear side and EPE on the front saw twice that rate of degradation (16%). EVA has been the most common encapsulant in the industry, in part due to its cost-effectiveness. The researchers said this problem was causes by a degradation pathway driven by magnesium additives in the EVA material, which hydrates under damp heat and “generates an alkaline micro-environment” that allows moisture ingress into the polysilicon layers of the module.

“Notably, there was no consistent trend in degradation behaviour associated with different encapsulant types on the front side,” the paper said in its conclusion, adding “it can be concluded that the modules with POE on the rear side showed relatively greater stability compared to those with white EVA on the rear side.”

“Despite the advantages, TOPCon modules still encounter notable reliability challenges under high-humidity conditions, particularly in glass/backsheet configurations, which can result in significant power degradation,” the paper said.

What other issues does TOPCon have?

Research from a number of leading institutions have pointed out the issues that TOPCon has with potential-induced degradation (PID) and UVID. A paper from last year by scientists at the Fraunhofer ISE in Germany found that TOPCon modules showed “critical” rates of degradation, undermining the long warranties often advertised by manufacturers. The paper’s lead author told PV Tech Premium that this comes down to the pace of change in the solar industry, which has resulted in TOPCon products have entered mass production without proper technical qualifications or checks.

This week, a separate paper authored by researchers from the National Renewable Energy Laboratory (NREL) in the US – now renamed the National Laboratory of the Rockies – looked further into the effects of UVID degradation on TOPCon modules, specifically how the products can degrade further in dark storage and show “rapid recovery under sunlight”. This, they said, complicates efforts to quantify the impact of UVID on TOPCon modules and cells. The paper, ‘UV-Induced Degradation and Associated Metastability in TOPCon Photovoltaic Modules: Understanding Kinetics and Cell Variance’, published in Progress In Photovoltaics, found that cell-by-cell degradation and recovery rates in modules exposed to UVID and then stored in the dark vary massively, from +6% to -70%.

Is the industry responding to the problem?

Some studies have suggested that there have been improvements in the last year. A report from Kiwa PI Berlin last week on PV module manufacturing quality said “cell-related defects in TOPCon production have decreased” over the last year, “and are now comparable to those observed in PERC modules”. PI Berlin attributed that improvement to improved cell-level design, material modifications and growing expertise in TOPCon cell manufacturing.

The same report also said that defects in module production vary by region, with the US showing the highest rate of defect incidents, and more established PV manufacturing nations like Vietnam and Indonesia – where major Chinese players operate – performing better. This is even true within individual manufacturers, PI Berlin’s report said, with products from the same brand varying in quality depending on where they are produced.

Some of this variation is due to supply chain disruptions triggered by trade policies and geopolitical wrangling. The US, for example, has rushed to establish a solar supply chain over the last two-to-three years, with significant module manufacturing expansions and a slow dripfeed of cell capacity. We know that new factories have higher defect rates, and even modules produced on a night shift have shown higher defects than those produced in daylight hours at the same facility.

But from a technological standpoint, the onus might be on developers and module buyers to push for greater quality assurance. Steven Xeureb of PI Berlin told PV Tech Premium that developers and investors should be pushing their suppliers for as much transparency as possible, and invest in quality to avoid issues down the line.