Senior leadership of the world's largest solar PV manufacturer, LONGi — Founder and President LONGi Green Energy Technology, Li Zhenguo and Vice President, Central R&D Institute LONGi, Dr Xu Xixiang — discussed the company's various technological breakthroughs during TaiyangNews Virtual Conference on High Efficiency Solar Technologies 2022 – TOPCon, HJT and Beyond, Today & Tomorrow, including its solar cell world record of 26.81% with TaiyangNews Managing Director Michael Schmela. Here is an excerpt.
TaiyangNews: Getting straight to the point, what have you done to improve your latest record cell to 26.81%?
Xu Xixiang: I think there are three factors. First, we optimized our intrinsic amorphous silicon layers as passivation layers and further improved that. For example, we made multiple layers. Even though it is very thin about 5 nm, they have different functions. In the previous layer, we had more hydrogen, better passivation. Later on, we strove to keep it as a good quality amorphous silicon. In that way, we lowered the deposition rate. In order to avoid epitaxial texture growth, people will use very high deposition rates of amorphous silicon. However, we recognize that with very high rates, the quality will not be optimum. That's why we did this – multiple layers for intrinsic layer.
The second factor is doped layers: N-layers and P-layers. As I mentioned, we use nanocrystalline – N and P. N is for silicon and oxygen alloy…to widen its band gap as a better window layer to absorb less light. In this way, we have high current. It is significant that we were successful in developing the nanocrystalline P layer this way. Because we did this kind of work three times before, but it did not work. However, this time around, we made this manufacturable, large area, nanocrystalline P-layer.
And the third one, I think is that we developed a new process for TCO transparent conductive oxide. This move is also critical because this gave us a high fill factor. Basically, the Institute for Solar Energy Research in Hamelin (ISFH) measured a very high fill factor. At first, they doubted, wondering if they have done something wrong, because the highest fill factor we achieved was 86.59%. That is the champion of fill factor.
TaiyangNews: Super. It looks like you're on a on a record-breaking mission. We've seen so many new records from you recently. How important are cell and module records for LONGi? And how is it possible that you almost have a record-breaking factory at technology?
Xu Xixiang: Yeah, actually LONGi is working at the same time on multiple technologies. Not only are we working on HJT or TOPCon or IBC, but also on other technologies – depending on cost competitive products, the application and environment. So, we come up with different products. We have N-type Topcon. The record in the industry last year was 25.21%. Then we have the P-type TOPCon product at 25.19%, led by Dr Li. Then we achieved the n-type HJT and the p-type HJT records. At the same time, we also reported a indium-free TCO record cell.
TaiyangNews: Let's talk a little bit about p-type versus n-type? I think there is this trend now in the industry. Most companies are going n-type, but you have always been a strong promoter of p-type. You are the world's largest wafer manufacturer. Can you just shine some light on that? How do you see the developments in the change from p-type versus n-type?
Xu Xixiang: Historically, the efficiency gap between n-type and p-type was bigger – probably 0.5 to 1.0% absolute difference. But now, LONGi is producing better quality p-type wafers. In fact, the whole industry is producing. Earlier, we published a summary about p-type TOPCon and n-type TOPCon, p-type HJT and n-type HJT. The difference was not that big. We are also working on p-type HJT and that efficiency is actually quite close to n-type. So that's a good option. And if we look at it, a silicon n-type wafer is more expensive. If you have a 5 to 6% difference in terms of cost between p-type and n-type, that's a big deal. But in future, as we believe and as President Li has often mentioned, the cost of n-type silicon wafer will go down, eventually. The cost difference will be smaller. And I think the technology on both wafers are getting closer.
TaiyangNews: We are tracking efficiencies very closely in our monthly TOP Modules listing and it's really interesting to note how far the p-type module, even the p-type module PERC efficiencies have come – with commercial ones now touching an efficiency of 21.7%. It's truly amazing. A lot of people would have not estimated this. So, what is the future for PERC, now that it has 21.7% efficiency on the module level? Is that the limit? Or is there some leeway to improve it?
Li Zhenguo: For PERC, the potential is not that much. However, this technology is a next-generation technology and can be combined with other technologies, just like HPBC. We actually have PERC technology trends in HPBC. With PERC cell efficiency touching 24%, moving further up may be difficult, but with other combinations like PERC Plus, we think there is still potential and LONGi has been active in that area. Second, we believe that the cost infrastructure is not a key issue for PERC. The cost of non-silicon wafer component is already at $0.02. Driving down this cost further is not the key for the PV industry, or for the LCOE because it is already at a low-cost price. Rather what's important is improving the quality. This will build the foundation for new technical roots for the silicon wafer.
TaiyangNews: Where do you see the key cost-reduction potential in the next round? What has been the biggest impact on cutting costs further on the module side?
Li Zhenguo: For a PV power generation system, around 70% is actually protection material for the solar cells, which includes cover glass, aluminum framing, encapsulation foils and other devices that are used for grid-connection. The best way to drop the cost is to improve efficiency as it can reduce the impact of cost-increase in other parts too. Hence, we focus on improving the efficiency conversion, first, for mass production of n-type silicon wafers, and in the next phase, we want to mass produce with 27% efficiency, and with two layered silicon wafers. We have suffered from irrational fluctuation of wafer prices, which however accounted only for 25% of the cost-increase. Hence it is necessary to concentrate on other parts too for cost reduction. And towards that, our focus will strongly remain on efficiency improvement.
TaiyangNews: When we talk about efficiency and tandem cells, we also have to talk about perovskites. There are lot of activities in China on perovskite, while many research institutes in Europe are working on Si-Perovskite tandem cells. When will we see the first commercial tandem products coming into the markets? And what is LONGi's activity in this field?
Li Zhenguo: LONGi is a public limited company. Hence, before we make a public announcement, we are not at a liberty to disclose any such information. But we have a pilot of 2-3 MW scale of this and HJT. That's all I can disclose for now.
TaiyangNews: Okay, I understand. Well, a final question that goes beyond technology, and focuses on supply and demand. The market is growing much faster than any analyst predicted. And this goes year after year. At the World Conference in Milan, you showed this learning curve that the market could reach 1 TW per year by 2030. This is the learning curve and somewhat theoretical. It can change obviously, get a little bit steeper, a little bit flatter. But do you think that we can grow to 1 TW per year of installations by 2030?
Li Zhenguo: Actually, I am very optimistic for the PV sector. And even with such optimism, let me admit, I did not expect this rapid progress of the market needs. Also, we did not expect a consensus on carbon neutrality this early on. We are making efforts to contribute to carbon neutrality, but we did not expect to face the consequences so fast and early. This has led to a rapid and strong momentum for market demand, which in turn has led to price hikes of the crystalline wafer. The price hikes have been irrational at times, leading to issues for market participants.
As to your question, if we can achieve 1 TW – yes we can and it will be achieved as long as each country takes carbon neutrality seriously, and not treat it as a joke. At the same time, our world should also avoid extremism like war. With that in mind, we can achieve 1 TW installation by 2030. Only by achieving the TW level can we make significant or logistic contribution to carbon neutrality.
From a supply perspective too, it is doable because the resources are not limited. Let's trace back to the primitive energy resources. The PV sector requires the same resources and labour like, for instance, silver paste, aluminum framing, and other steel materials. Even when we meet the TW level, there will be enough supply of these materials. With such market conditions where there is no resource limitation, the TW era can surely be achieved. Moreover, achieving TW is inevitable and important as it will be a great support for carbon neutrality.
TaiyangNews: Thank you for the interview
The interview can be also viewed on TaiyangNews' YouTube channel, click here.