Heraeus Photovoltaics is the global market leader for silver pastes. A global business unit of German specialty materials company Heraeus Holding, it manufacturers its products mainly in Asia close to its customers. TaiyangNews Michael Schmela & Shravan Chunduri talked to Weiming Zhang, CTO of Heraeus Photovoltaics, about the strategy on how to maintain its #1 rank in the silver paste business and his view on the market and technology development in metallization.


TaiyangNews: How does the market leader in the field of solar cell metallization look at the current solar market development?

Weiming Zhang: We are overall quite optimistic about the market environment this year – and also for the next few years, even though we expect a few ups and downs. We expect to have 122 GW in 2018. The Chinese PV sector recently published its Q1/2018 results and distributed installations increased about 217% compared to Q1/2017. This is great news. In China, 2018 demand will be around 45 to 60 GW. We also think that the second largest market India will grow to 11 GW this year. The fact that we see the number of 1-GW-markets growing to over a dozen this year keeps us optimistic.

 TaiyangNews: Competition is increasing in the metallization segment. For years there was only a handful of players sharing the segment among each other. That has changed. As of recently, a lot of Chinese suppliers have been moving into solar cell metallization – first, they were only present in back side metallization and now they are also competing for the front side silver pastes segment. What is your strategy to remain a market leader?

Weiming Zhang: Competition is good for the industry; it is the nature of every business – and we believe that the PV industry definitely benefits from it. But you are right, a few years ago, there were 2, 3 or 4 paste suppliers, and now there are many. However, if you look back, you can see clearly that many companies come and go. I don’t know how our competitors are looking at this industry, but Heraeus is very committed to PV, which we entered 10 years ago.

We anticipate that competition will even further grow, because metallization is one of the key application areas that enable the PV industry’s continuous growth. So the crucial question is who is able to serve customers with leading technology in the long run.

 TaiyangNews: But what’s your concrete strategy to stay a leader? Smaller, new companies have lower overheads while the metallization business is not very capex intensive, it does not cost too much to buy mills and mixers.

Weiming Zhang: Actually, our strategy is very simple: we look at the pipeline and we have a broad portfolio. This allows us to support our key partners for attaining technology leadership. We will keep investing in innovation to maintain our technology leadership. Performance and efficiency are still the key drivers for market success over costs.

The second topic is customization. We were the first ones that came up with a strategy of customizing products many years ago, when others had very different views. That allowed each of our key customers to differentiate their process and technology from competition. Heraeus’ service is very much valued.Last but not least, although the silver paste business is not capex intensive, it is capital intensive in terms of the precious metal component of the working capital. Being the largest precious metal company in the world means that we can offer PM related services to our customers.

TaiyangNews: The more the Chinese solar industry grows, the more areas in the production value chain are taken over by domestic companies. How are you addressing this development as a German company?

Weiming Zhang: Being part of Heraeus Holding we do have access to a very broad spectrum of different technologies that we can leverage for our pastes business. Even though our Holding is located in Germany our PV business is headquartered in Shanghai and a majority of our investments are done in China. From our customers’ perspective we offer the benefit of a local company combined with a global background.

I also still strongly believe that the PV industry and cell manufacturers are not just looking at costs. It is not like a regular consumer electronic product.Of course, cost is very important, but there is more than that. The industry needs technology leadership, quality products, high performance, consistency and sustainability – that’s how we try to serve our customers.

TaiyangNews: The solar world moves in the direction of monocrystalline cell technology and PERC has become the new mono standard. What cell technologies do you see dominating the market in the next 10 years and why?

Weiming Zhang: Indeed, PERC has become mainstream. And I don’t think that PERC technology has exhausted its potential yet. You are going to see new developments and upgrades to PERC to reach higher efficiencies. We have  already seen bifacial technology. After PERC, cell technology would naturally progress towards n-type, but it will take a little more time than expected, even though we clearly see the performance advantage of n-type. I also believe that passivated contacts (TOPCON) would be a natural progression. So in short, we will first see PERC upgrade, then n-type and next heterojunction in the coming 10 years.

TaiyangNews: So when will we see the first big n-type capex investments?

Weiming Zhang: Originally, we also expected n-type will come earlier. Because of PERC’s progress, n-type is currently a bit under pressure. But it will take off, particularly in China due to the Top Runner program. We have already seen strong interest from our customers for our n-type products. However, it is hard to tell  exactly when n-type will really come big – maybe in 3 or 5 years.

TaiyangNews: You also mentioned the passivated contacts approach. How far away is this TOPCON technology from market introduction?

Weiming Zhang: I think it is not that far away. At Heraeus, we started product development ~1.5 years ago. We are working with industrial and academic partners and have already solved some fundamental issues with metallization for TOPCON cells. Our first R&D paste samples have already sent to our partners and quite soon we will materialize a paste solution for this application. Of course, we start with n-type cells application first, but it will be gradually implemented on p-type technology as well.

TaiyangNews: Do you see TOPCON to enter mass production earlier than heterojunction cells?

Weiming Zhang: Yes, TOPCON has the potential for quick adaptation in the industry, because it requires less investment and offers the possibility to upgrade current production lines.

TaiyangNews: Earlier, PERC design was following the emitter of the standard cell structure, where contacting increasingly high sheet resistance emitters was the main task. With PERC now moving towards selective emitters, it relaxes the PERC emitters paste from the high resistance emitters requirement. What are the driving forces for PERC emitter pastes with selective emitters?

Weiming Zhang: We also see that several big players are looking into selective emitters. While the metallization part of SE is generally less demanding in terms of contact, there are other challenges. Our new generation 9651 series are specially designed for the SE process. We fine-tuned the glass chemistry and paste chemistry for SE. While lasers are most popular to produce SE cells, each customer needs some customization due to their own process control. We also have key customers who insist to get pastes for lightly doped emitters for their PERC process. So we continue to work on pastes for contacting lightly doped emitters as well.

TaiyangNews: What are the next gen technologies you are focussing on at your product level?

Weiming Zhang: We definitely put a lot of development work on pastes for PERC and for DWC multi. We also invest in new technologies – TOPCON, n-type and heterojunction are the high efficiency cell technologies we are trying to expand in our product portfolio.

TaiyangNews: You just mentioned multi. Don’t you think multi is doomed?

Weiming Zhang: I think it is too early to call it doomed or even dead. Mono is clearly taking larger leaps in terms of performance, on top comes lower wafer costs. But we cannot ignore the fact that there is still a lot development taking place within the multi segment – all the way from ingots to wafers to cells. GCL, for example, is pushing DWS multi with black silicon in combination with PERC. Or on the ingot level, one of our non-silver paste products is contributing to multi ingot efficiency improvement and yield. Long story short: Multi is still going to see cost improvements.

TaiyangNews: Cost pressure is not going away, in fact it will get even worse with countries moving to competitive tenders and solar starting to compete with wholesale power prices. How can metallization contribute to further cost reduction?

Weiming Zhang: We need metallization to facilitate higher efficiencies at cell manufacturing. This is definitely one level, which will continue. A second development to continue is the push for low laydown – lower paste usage and silver usage per cell and per watt. In 2018, it is very likely that average paste usage could reach about 90 to 95 mg, down from about 100 to 105 mg last year. For 2019 we expect 85 mg and in 2020, we anticipate 75 mg. In order to enable this lower laydown, paste technology, screen technology and equipment have to improve collectively. A new technology may also be required to realize this goal. Third, Heraeus has always been looking on how to optimize our operation and our internal cost structure.

TaiyangNews: But the air is getting thinner for material reduction and will require more efforts…

Weiming Zhang: I am quite confident to see further improvements, which is also our key focus area. For instance, in 2018, the average finger opening in single printing is ~30 µm. But with double printing it is possible to go down to 22 to 24 µm today. And there is more potential. Even single printing can go down to less than 25 µm finger opening, and for double printing we see a potential of 16 µm. All this will contribute to lower laydown. Then there is further support from the industry’s move to a higher number of busbars – 6 and even 12.

 TaiyangNews: What do you expect from screen printers?

Weiming Zhang: Manufacturers of paste, screen and printers have to work together. We all face the same challenges as we work toward our goals of continuing to reduce finger openings and paste consumption. Customers are also demanding high process control, for example EL images. Screen printer manufacturers are under pressure to improve throughput. The printing speed used to be 200 or 250 mm/s, now it is 400 to 450 mm/s. I would not be surprised if we see 500 or 550 mm/s and cycle times below 1 second soon. In turn, this would mean that pastes would need to be upgraded.

TaiyangNews: And how do you see the developments at screen level?

Weiming Zhang: Screen technology is also improving, especially with high meshes. A 480 / 11 µm mesh screen has started entering the market, though in small production volumes. Such screen technologies will definitely help in finger opening reduction and savings in paste usage

TaiyangNews: What’s your view on knotless screens?

Weiming Zhang: Knotless screen have been established as a technology approach for cell makers that are still using single printing. Some companies have adapted knotless technology, but interestingly not all. There seems to be still some disadvantages of knotless compared to high mesh screens. One is screen lifetime and thus cost. Cell manufacturers are pushing lifetime of screens to levels as high as 100,000 prints, which is very difficult for knotless to reach due to its intrinsic structure. In addition, knotless has some appearance issues when employed with monocrystalline cells. These cosmetic issues with knotless and recent improvements for high mesh screen technology have even attracted some cell makers to switch back to high mesh from knotless.

TaiyangNews: Another attractive screen printing method is double printing, but we’ve heard that it has a share of only 15 to 20%. Why is it so low?

Weiming Zhang: I think double printing will continue to be used by those cell makers who can take advantage of this technology on the operational side and the technology side. That is why Heraeus is committed to develop and deliver our next generation double printing paste for those customers. And it is amazing to see how some cell makers are able to push and leverage double printing technology. On the other hand, some companies are taking advantage of other developments in screen technology – high meshes and knotless, which is another approach to balance cost and performance. Thus some will continue to use dual printing and single printing technology. However, for double printing there is a certain benefit that cannot be achieved from single printing and dual printing.

TaiyangNews: Product life cycles are diminishing a lot and as you mentioned earlier customization is becoming increasingly prominent. How do you handle this rather ‘costly’ development?

Weiming Zhang: We are actually well positioned with our customization strategy. When we started to push this idea a few years ago, we already prepared for this. That is why we set up R&D facilities in Shanghai and in Taiwan. We are also setting up R&D in Singapore area to serve our customer base in South East Asia. It is definitely a costly affair, but it brings great benefit to the customer. Meanwhile this also shows our commitment to this industry. In our R&D centers, we develop new and advanced generation platforms and keep them in our pipeline, much ahead of the industry.

TaiyangNews: You signed a strategic partnership with the world’s largest module supplier JinkoSolar last year? How is this working out?

Weiming Zhang: We value this partnership with JinkoSolar very much. JinkoSolar is not only the largest in shipments two times in a row, they are also a leader on the technology front. In return, we give them our best support. Our latest generation paste 9561 is currently being ramped up at JinkoSolar. Being our strategic partner, JinkoSolar can be the first to benefit of our latest product generation that we developed together. The partnership also significantly reduces our development and cycle time. As a partner, straightforward and best customization of the newer generation of paste takes place with JinkoSolar.

TaiyangNews: Is the partnership with JinkoSolar exclusive or are you also open to other companies for strategic partnerships?   

Weiming Zhang: We are also working with many other big customers and with a few through strategic partnerships as well. Every big customer needs a focussed customized metallization solution. For example, the 9651x is a new generation platform and the suffixes are customized variants specifically made to suit a particular cell maker’s process requirement. One of those we offer for double printing.

TaiyangNews: Heraeus is apparently also looking beyond pastes. Last year you signed a partnership agreement with solar ribbon manufacturer Ulbrich. Why?

Weiming Zhang: This is part of our “beyond silver pastes campaign” strategy. Heraeus has 9 business units and each has very deep knowledge and technology offering. At Heraeus Photovoltaic, we try to leverage from the technology offering from other branches. Selective coating ribbons is one example that we leverage. The other is, as I mentioned before, the solution from Heraeus for multicrystalline ingot making – Heraglaze.

We also see that we can provide more solutions for our customers beyond silver paste. Eventually we would like to be a solution provider that offers several bundles – product bundles and service bundles. This can save our customers time and money. This is part of our ‘beyond silver paste strategy.’

TaiyangNews: When you talk about your ‘beyond silver strategy, what do you think could be a disruption for silver in metallization for solar cells in next 10 years?

Weiming Zhang: As for metallization, I don’t think silver is going to be out of mainstream as it will provide the performance improvements required by the solar industry. Of course, plating has always been on the wish list of the industry. But with all the evolutionary developments I mentioned above, I am very confident that silver based metallization will fully dominate the metallization field at least for the next 5 years.

TaiyangNews: Even if silver remains the core, how are you looking at aluminum pastes? There is a lot happening in this area. When you acquired the IP from Ferro, they were developing a fire though paste for a p-type surface. Now some companies are also working on this approach. Will you look back into aluminum pastes again?

Weiming Zhang: From the technology side, we definitely see n-PERT and PERC bifacial coming. Here we see potential for aluminum paste to be differentiated on technology and product performance. For n-PERT, aluminum is uniquely positioned. For BSF aluminum, on the other hand, there is not too much to differentiate.

TaiyangNews: Thank you for the interview.


The interview is from the TaiyangNews Market Survey on Metallization Pastes 2018, which is for download here.