HJT Technology Is Ready!

TaiyangNews: Meyer Burger is promoting HJT very vigorously these days. What are the key drivers for the technology?

Gunter Erfurt: There are 3 elements when it comes to choosing technologies for PV systems
– the technology push resulting from Chinese government’s 5/31 directive to restructure its solar support program; the readiness of the technology, and the market pull effect which is increasingly coming from utility companies and EPCs who are interested in best levelized cost of energy (LCOE).

HJT is ready in terms of both process developments, as well as capex and cost of ownership. There is a rapidly increasing interest in the market that we are witnessing – a change in perspective from dollars-per-watt peak toward LCOE. More and more pull from the market for solutions with low LCOE will speak for HJT.

TaiyangNews: You said there is a growing acceptance for HJT from end users?

Gunter Erfurt: Indeed. More and more energy utility companies and the middle-men such as the EPCs – are playing a decisive role in today’s PV market. When they learn about the benefits of HJT, such as low-temperature coefficient, low-light performance and bifaciality, their acceptance and interest increase significantly.

TaiyangNews: And what does China’s solar program restructuring effort have to do with HJT development?

Gunter Erfurt: Well, the 5/31 impact has not only been on China’s market, but the global market as well. However, China has reduced support for large- scale ground-mount systems, which are generally built with lower-efficiency modules; but they have continued their Top Runner Program to incentivise high-efficiency cell technologies; even in times of restructuring. Heterojunction cells are today among the highest efficiency solar cells.

The PV market is very dynamic. Just a year ago, PERC cell technology was viewed as a new technology, which definitely benefitted from the Top Runner Program. At the same time, the market viewed Al-BSF cells as commodity products. Today with its 50 to 60 GW of installed capacity, PERC is also becoming a commodity product. Some large manufacturers with extensive production capacities may continue to focus on a single technology and follow an evolutionary path, which could well be passivated contacts (TopCon). Meyer Burger will of course also support customers with this technology but we are convinced that HJT has a much higher potential.

TaiyangNews: So you expect the up and coming cell technology will be HJT?

Gunter Erfurt: Yes, we do. For both module manufacturers and end-customers, HJT has enormous inherent product USPs enabling them to produce more high efficiency products at similar costs as module manufacturers can achieve with PERC today. We believe that once the HJT production volumes increase, the cost of ownership of a scaled-up HJT line will not be higher than for PERC.

TaiyangNews: So what has really changed in the technology that makes it “ready for prime time”?

Gunter Erfurt: Even though Panasonic has been manufacturing HJT for decades, the technology had largely been stuck at the lab scale. However in the last 10 years, it has been developed further, and the costs structure has substantially improved. The readiness of the peripheral system, like handling tools, is also now in place; especially for PECVD, as handling of the amorphous silicon layers is challenging, compared to handling standard cells.

TaiyangNews: But making tools is one thing, reliable production is another?

Gunter Erfurt: That was one of the concerns in the market regarding a new technology like HJT. However, Meyer Burger has thoroughly tested the HJT line configuration, specifically PECVD and PVD. We ran about three million wafers and processed them into cells. We also built modules and made PV systems with customers to prove the performance of HJT solar panels. As a result – and this is just my opinion – HJT is probably one of the most thoroughly tested cell technologies available today.

TaiyangNews: What about efficiencies of the cells and modules?

Gunter Erfurt: Today Heterojunction cells deliver average efficiencies beyond 23% to 23.5%. When installed HJT capacities increase, further increases in efficiency are also bound to happen at a faster pace than we saw with the PERC technology because the level of optimization has already taken place with PERC, while with HJT we are just at the beginning.

TaiyangNews: But producers have to have confidence in the supply chain, don’t they?

Gunter Erfurt: That’s true. One of the major concerns of the industry has been the n-type wafer supply but technologically, it’s more or less a done deal. With the support of the leading manufacturers, we have helped bringing the material to the level where it is now an off-the-shelf standard wafer. If you had asked the same question 2 or 3 years back, my response would have been negative. Even the economies of scale would not have helped then, because the n-type wafer technology was simply not ready. That is no longer the case.

TaiyangNews: n-type wafers as the key ingredient are still more expensive today. How can this be changed?

Gunter Erfurt: According to leading wafer manufacturers, n-type wafers are currently about 8% more expensive due to a slightly lower manufacturing yield. However, the manufacturing or pulling process for n-type ingots is being continuously improved and I am convinced that it’s only a matter of time before n-type wafers will be at the same price level as p-type. Moreover, wafer makers have stated that each 10 μm reduction in wafer thickness leads to a cost reduction of 1 to 1.5 US cents per piece. Although we are still at 180 μm, the trend for HJT n-type wafers is going towards to 150 μm. This decrease of 30 μm results in a reduction of 3 to 4.5 US cents, making them cost competitive with p type wafers even at todays’ higher production cost for n-type wafers. It should also be noted that a reduction in thickness of p-type wafers is much more difficult to achieve than for n-type wafers.

TaiyangNews: Do you see a problem with soldering due to reduced wafer thickness?

Gunter Erfurt: When it comes to the high- temperature solar cell process for thin wafers, there are issues not only with the bowing of wafers and mechanical stress but in soldering as well. For example, a module with 120 μm PERC cells will face tremendous challenges in yield as well as in passing the IEC test because of the high temperature stringing process necessary to manufacture the module. HJT cells, on the other hand, do not show any bowing due to the low-temperature processing can be easily soldered, too, without increased yield loss. The trademarked process used by Meyer Burger, SmartWire Connection Technology (SWCT), plays the key role in enabling the use of thin wafers.

TaiyangNews: And the thinner, the better also for the wafer quality?

Gunter Erfurt: Yes, the less bulk you have in your cell structure, the better the influence is on the resulting cell as potential recombination losses originating from the bulk are getter smaller and the losses from the surface are gaining importance. Therefore, superior surface passivation leads to a larger overall benefit by using thinner wafers. The surface passivation of HJT approaches similar levels to those in the semiconductor industry levels – with J0 below 5 fA/cm2 combined on the front and backside. For thinner wafers, this results in higher Voc and higher operating voltage but reduced current due to less light absorption. Even with overall efficiency remaining, the cell-to-module resistance losses are reduced. In our initial measurements, we achieved between 3 and 5 W more just by thinning wafers from 180 μm to 120 μm. So less bulk from the wafer will mean more wattage for the HJT module – and reduced costs. A typical double win.

TaiyangNews: Coming back to the supply chain, what about pastes?

Gunter Erfurt: There is still a lot of room for improvement for low-temperature curing pastes. However custom-designed products and more cost reduction potential are definitely coming.

TaiyangNews: What about production complexity?                            

Gunter Erfurt: Well, in general, HJT cell production involves fewer process steps – wet-bench, CVD, PVD and printing. HJT has huge potential to improve further both in performance and in cost of ownership.

TaiyangNews: Unlike PERC, HJT requires a completely different manufacturing setup and expertise. So who are your targeted customers?

Gunter Erfurt: The first customers came from converting or replacing their a-Si thin-film production into HJT. Next, we are seeing interest coming from newcomers to the industry, who are aiming at increased profitability. For newcomers, HJT is a clear choice. Meanwhile, also established players invest into HJT. On 14 December 2018 we were able to announce a 600 MW HJT+SWCT deal with a well- established premium brand module manufacturer showing us that our HJT is gaining traction in the industry.

TaiyangNews: Which technology will be the winner, PERC and its extensions or HJT?

Gunter Erfurt: Both technologies will continue to exist. Scaling is key for HJT and advanced PERC will benefit from the huge installed base.

TaiyangNews: Does being an integrated wafer to module production equipment company help with the development of tools for HJT technology?

Gunter Erfurt: Yes it does. Both the quality of the wafer as well as the module technology are strategic factors and our SmartWire Connection Technology is definitely the key you need to open the heterojunction universe. It is fair to say that the busbar heterojunction module is not financially attractive to producers as long as the paste configuration is what it is – that means high silver content because of the low temperature characteristics. Soldering- based multi-busbar is a possible option, but also here the amount of silver needed is twice as high as with SWCT. Silver paste consumption is actually the second highest material cost factor in solar module manufacturing and therefore we believe that SWCT is the perfect solution to ensure silver cost reduction in cell manufacturing as well as to enable the use of ultra-thin wafers.

TaiyangNews: It took time for SWCT to get a foot into the market, but recently you even sold this product to HJT pioneer Panasonic.

Gunter Erfurt: Actually, in December we announced the sale of a combined 600 MW HJT cell and SWCT module line which really underscores the industrial readiness of the technology. Now we are promoting the next generation of our SmartWire Connection Technology where we have rethought the stringer design. We handle cells using a foil-wire assembly electrode and our latest generation SWCT stringer has now by far the smallest footprint in the market for stringers. We can string 2,500 cells per hour on less than 4 m2 of factory space. In a recent acceptance test for a customer, we surprised him with yield values in the stringing process way higher than requested by their tough cell breakage specification – which demonstrates clearly the potential of SWCT.

TaiyangNews: While Meyer Burger was for a while basically the only one offering HJT equipment, now there are a few others that have entered the scene. How are you addressing that new competition?

Gunter Erfurt: Being in a competitive environment actually generates creativity and good ideas in tool development. What I can say, as of today, Meyer Burger is by far offering the fastest deposition process – just 80 seconds, with a potential for further reduction. Our integrated, automated tools also enable a very short handling time. There is quite a difference between standard PV technologies, where different equipment can be put together and heterojunction where the success will be determined by the ability of suppliers to integrate the important elements of HJT into their processes. This will differentiate manufacturers in terms of the quality they deliver. Like any other company, Meyer Burger does benchmarking with competitors’ products and we see the progress being made but we remain convinced that we can enable the leading combination of highest efficiency manufacturing technologies at competitive costs. Meyer Burger’s advantage with HJT lies in the process integration, which means fine-tuning the different manufacturing steps. We were able to test extensively and gain enormous experience, which now gives us a head start in the market. Currently, Meyer Burger is the only company able to demonstrate module performance using its own HJT technology.

TaiyangNews: What is in store for HJT to take it to the next level?

Gunter Erfurt: With HJT the technology for silicon- based cell technology approaching its practical limits of 25% in mass manufacturing. The natural next step beyond HJT could be tandem structures such as HJT combined with perovskite.

TaiyangNews: Thank you for the interview.

This interview was originally published in our first TaiyangNews Heterojunction Solar Technology Report, which was released in March 2019 and can be downloaded for free here.