N-type Is The Way To Go & TOPCon Is The Choice For Now

TOPCon has become a buzzword in the PV community. Several companies have been announcing gigantic plans with the technology and few have made their first move with Astronergy being one among them. The company not only has a very ambitious plan to reach 23 GW TOPCon capacity by the end of next year, Astronergy has also commissioned its first production line with 4 GW capacity and started production.

TaiyangNews visited TOPCon production facility of the company at Astronergy Industrial Park in Haining, Zhejiang province, China and interviewed the top executives of the company— CTO Alex Hsu, R&D Director He Sheng and Product Director Jack Zhou. That is why we have not attributed the answers to one person in particular. Here are the excerpts from those various conversations:

TaiyangNews: The key players of PV are heavily discussing n-type, be it HJT and TOPCon; does this mean p-type PERC has hit its limit?

Astronergy: What I can say is that the end of PERC has started, but not the p-type as such. As you may be aware one big PV manufacturer has been working on commercializing IBC cell architecture based on p-type. However, several PV manufacturers are moving to n-type. So, I can also say that n-type era has started at the same time.

TaiyangNews: Historically, the market adapts to new technologies during the slump, but PV is very hot now and is expected to get hotter. Why are companies in a rush to explore new technologies, when one could practically sell everything in today's market?

Astronergy: PV as an industry, we as a leading manufacturer of the segment, cannot simply rely on present. Yes, the market is good, and PERC still has the lowest cost. What's important when it comes to costs is that there are direct costs and then there is the performance, which has a significant impact on indirect costs. What I want to say here is that increasing efficiency indirectly reduces costs. But PERC has almost reached its limit, especially in terms of performance, with only a little more potential to reduce costs further. This indicates PERC has a very little room left for further cost reduction. This is typically the time, like for any other progressive industry, for PV to seriously evaluate alternate technologies. This is exactly what the industry is doing. It is absolutely apt in terms of timing.

TaiyangNews: TOPCon and HJT are two high efficiency routes. It is obvious you took TOPCon direction; what is the reason?

Astronergy: I just want to say that while we did choose TOPCon at this stage, we never gave up the research of other technologies like HJT, IBC etc. The costs of TOPCon would be comparable to PERC by end of this year. This is a big reason for us to select TOPCon technology at present stage. The costs for HJT are much higher than PERC, and also above TOPCon. We actually do not see a very reliable method to reduce costs of HJT significantly in a short period of time.

TaiyangNews: Are you also operating or have plans for any pilot project with HJT or any other advanced cell architecture apart from TOPCon?

Astronergy: Our main focus for production is TOPCon, but we will also prepare for HJT and IBC at R&D level. And, we will work on both p-type and n-type IBC.

TaiyangNews: At first glance it is very clear that TOPCon has higher costs as it requires double the amount of silver, processing steps are more complex and is based on n-type wafers that are expensive than p-type. What are the cost reduction avenues that enable TOPCon to be at par with PERC?

Astronergy: The first and foremost is the higher efficiency that reflects in higher module power. The superior electrical parameters compensate higher costs to a large extent. Coming to wafers, we have now reduced the wafer thickness to 140 µm, which compensates for the higher costs of the n-type wafer. That's because PERC still uses relatively thicker wafers than TOPCon, and since the latter has no laser scribing involved in processing, it supports wafer thickness reduction. At this level, costs of thinner n-type wafers used for TOPCon are similar to the slightly thicker p-type wafer used for PERC. On top, with our next generations, we will also reduce the wafer thickness further to say 135 µm and 130 µm, which would additionally reduce wafer costs. Paste weight reduction is very critical for TOPCon cost reduction. In the beginning, the paste consumption with TOPCon was 150 mg, which is already reduced to 110 mg level now, while PERC metallization currently requires 60 mg per a M10 wafer. However, we have a strategy in place to reduce the silver usage in steps, down to 80 mg, there by narrowing the gap to PERC.

TaiyangNews: What should be the efficiency of the TOPCon cell that can compensate all additional costs?

Astronergy: The numbers vary from company to company as there are several assumptions involved in such calculations. However, on a general note 1.5% to 2.0% absolute higher over the PERC can easily compensate the additional costs of TOPCon. Considering PERC efficiency is at 23.5%, TOPCon efficiency should be at least at 25% to be directly cost competitive.

TaiyangNews: What is your current capacity for TOPCon and have you installed any pilot line for HJT?

Astronergy: Our total n-type capacity as of now is just TOPCon, which would be 4 GW by end of this year. We just also started the preparation for HJT R&D/pilot line. We also have some leverage over others as Ideal Energy, which has a long track record of making PECVD tools for HJT and Astronergy's parent company CHINT Group is controlling shareholder Ideal Energy. So yes, for now TOPCon is our focus, but we will equally focus on HJT and when the technology is ready, we will take it to the next level.

TaiyangNews: What are your expansions plans with TOPCon?

Astronergy: We are pretty serious with the technology. We started mass production and reached 24.9% in mass production already. As I just mentioned, we will reach 4 GW capacity for TOPCon by end of this year. Next year we will increase the n-type cell production capacity to 23 GW, most of which would be TOPCon. Our total cell production capacity including PERC by then would be 35 GW.

TaiyangNews: Compared to the past, what has really changed with TOPCon technology that we see a lot of companies of late taking keen interest in the technology?

Astronergy: First is efficiency. PERC efficiency stayed less than or equal to 23.5% more or less. On the other hand, the efficiency of TOPCon went up from 24% to 24.8% to 25% in one year. Next is costs. Of course, several aspects contribute to costs. One is wafer thickness reduction; I already explained that TOPCon has achieved a competitive level and holds great potential for further reduction. The progress and potential for silver paste reduction is yet another key driver. The close resemblance to PERC production line is among the top. 

TaiyangNews: What are the major bottlenecks with TOPCon that still have to be addressed?

Astronergy: There are three key limitations. One is boron oxygen cycle. Since it is a n-type wafer, its emitter formation is done by boron diffusion process. Due to the high affinity of boron and oxygen, boron escapes from the wafer easily with oxygen, making the diffusion process unstable.

The second is the wrap around, especially when using LPCVD. The third one is the yield, which across the industry is a little lower than PERC.

TaiyangNews: What is the status of the current supply chain for TOPCon – production equipment, deposition technologies and metallization pastes?

Astronergy: We consider this as the first year for TOPCon. That's because the supply chain is ready – be it the process, production equipment and even silver pastes. There are different tools vendors offering various deposition technologies and these tools are ready and so are the pastes.

TaiyangNews: Can you comment on the deposition technologies you are employing for the application of tunneling oxide and poly for TOPCon?

Astronergy: We use LPCVD. The quality of both the tunnelling and polysilicon layers is good with the LPCVD. Simultaneously, we are also paying close attention to PECVD and its development. Though its quality is not at par with LPCVD, PECVD realizes higher deposition rates, thus supports higher throughput.

TaiyangNews: How are you addressing the wrap around?

Astronergy: While I cannot completely disclose the approach we are following, there are two ways. One is the placement of wafers in back-to-back position and just one wafer per slot. Each method has its own benefit. The back-to-back loading supports higher throughput, but wrap around and the corresponding chemical etching process is quite dynamic. With one wafer per slot, it is not difficult to design the process to remove the poly on front.  However, very soon there would a standard approach on how to deal with wrap around.

TaiyangNews: Can you comment on the bifaciality of TOPCon structure? What is your spec for bifaciality?

Astronergy: High bifaciality is a key attribute of TOPCon that gives the technology a premium over PERC. We can attain 80% to 85% bifaciality at cell level and lower end of this range at module level. This is about 10% difference over PERC.

TaiyangNews: How much would be the difference in power yield with this 10% higher bifaciality?

Astronergy: Depending on the ground albedo, the gain in power yield ranges between 1% to 5%.

TaiyangNews: When it comes to the bifaciality for TOPCon, there is a fundamental limitation of some absorption in the polysilicon layer. How can one improve it further?

Astronergy: There are 3 ways to optimize the bifaciality of TOPCon. The first one is optimizing the metallization pattern, especially reducing the fingers width and busbars on rear side. Adjusting the silicon nitride layer on the rear side for optical properties is the second approach. Increasing transparency of rear glass is yet another way to boost the bifaciality.

TaiyangNews: What is your current champion and average cell efficiency?

Astronergy: We have achieved 24.9% average efficiency for the champion batch and best R&D efficiency is 25.2%.

TaiyangNews: What are the targeted markets for your TOPCon product range – primarily rooftop or utility segments?

Astronergy: Our ASTRO N series has products addressing the needs of various segments of the market. The first one is ASTRO N 5s, which is mainly designed for rooftop application, especially for the overseas markets as the module is also offered as all-black variant. The ASTRO N5, based on 182 mm wafer size with a power rating of 570 W, is mainly promoted for C&I segment.

TaiyangNews: What do you think will be the global production capacity of TOPCon by end of this year, and next year?

Astronergy: We are also relying on external data for this. For example, PVInfolink estimates that TOPCon capacity would reach 75 GW by end of this year and 130 GW by end of next year.

TaiyangNews: Thank you for the interview.