After an insightful day 1 of TaiyangNews annual flagship event High Efficiency Solar Technologies Virtual Conference where focus was on TOPCon technology, day 2 on December 14, 2023 revolved around heterojunction (HJT).
In a keynote address, Vice President of the Swiss research and development center CSEM, Christophe Ballif gave an update on the progress of HJT technology.
HJT cells were commercially made available by Japan's Sanyo in the early 2000s. Later, this technology traveled to Europe and the US, and finally to China.
Reflecting on the technology's growth over various decades, Ballif went back to the 2nd HJT workshop in 2019 in Chengdu when it was determined that HJT cells have the potential to reach 25% efficiency with process adaptation and reduced thickness to 110 microns, but CapEx was seen as the strongest challenge along with paste and ITO consumption. Back then, it was assumed that while HJT may be ready for mass production, it won't be able to compete against PERC.
Since then, 4 years later, the global HJT production technology has expanded to 50 GW, shared Ballif. This expansion is not without technology improvements along the way, for instance availability of high-performance mass production equipment, that's also affordable now, silver use has come down and so has wafer thickness, all of which have contributed to boosting its power output.
Despite these advances, Ballif lists challenges for laboratory R&D on HJT, without pilot lines or funding. In the absence of these critical tools, research remains limited in terms of indium and silver usage, UV-light degradation, as well as reliability aspects.
In view of these factors, Ballif believes TOPCon will be the leading technology in the near future, while HJT offers potential in HBC and perovskite tandem arrangement.
Chinese HJT manufacturer Huasun Energy's Director of Business Development Europe, Christian Comes talked about how HJT helps meet the 3 key goals of high efficiency, GW-scale production and sustainability.
HJT was a much desirable technology since 2018, but it was costly, which made it a niche product. Now in 2023, HJT costs have gone down while efficiency has gone up. Yet, it remains costlier than the darling of the moment, TOPCon, even though the gap has reduced.
Comes claims that HJT modules currently being sold have higher efficiencies of up to 23% and power ratings over TOPCon counterparts. With regard to temperature loss and bifaciality parameters, which help determine module performance on the field, HJT is better than TOPCon. Improvements in module performance have a larger effect on LCOE while improvements in efficiency have a larger effect on BoS cost, explained Comes.
In 2008, module costs made up more than 50% of the total system cost but it has come down today significantly, as BoS costs dominate the same.
Since 2021, Huasun has been working on a number of areas to improve yield and efficiency as well with the use of thinner wafers and light conversion films, among others. As these factors improve module reliability, more and more HJT modules are being deployed across the globe.
Comes believes that just as TOPCon pushed out mono PERC out of the utility market, HJT will enter the utility-scale market in very huge volumes in the next 12 months. He sees the cost of HJT to be lower than TOPCon by 2025, and that's when substitution can take place.
Risen Energy's Senior Product Manager Jiajun Ye shared the Chinese solar PV manufacturer's experience with scaling up cost-optimized HJT production.
The company launched its 1st HJT module in 2019 with an output of up to 355 W. In 2022, it expanded the portfolio with its 700 W Hyper-ion HJT panel. Since then, the manufacturer has cut down wafer thickness from 150 µm to 100 µm which reduces the use of raw materials and improves reliability, according to Ye. Risen now targets to achieve 80 µm ultra-thin silicon wafers for 210 mm technology.
Reduction in wafer thickness is significant in HJT cell performance as it impacts light absorption. It also boosts cell flexibility as Risen found with 90 µm HJT cells remaining intact after maximum load test, compared to deformation in PERC cell (150 µm) and TOPCon cell (130 µm).
Ye shared the company's metallization technology roadmap to show it reduced metallization costs with low silver use for Hyper-ion HJT modules to $0.0102 /W till Q3/2023 and will bring it further down to $0.0064 /W by next year.
Risen will also bring down silver content by 45% in Q4/2023, and further down to 39% in Q2/2024 while increasing screen print speed to 375 mm/s and to 425 mm/s by respective target quarters.
Solar cell paste supplier Fusion had its Tech Director of HJT Ocean Tang talk about the progress in the development of the manufacturer's HJT paste.
Tang said currently HJT paste cost is 30% higher than TOPCon and 80% higher than PERC. This is owing to high laydown, a long process time in terms of printing speed and curing time, and low contribution to efficiency with wide line-width for high conductivity.
According to Fusion, HJT cell's high production cost can be lowered in several ways such as with the use of silver coated copper (Cu-Ag) paste, narrowing screen opening from 17 µm to 15 µm, and using zero busbar cell (ZBB). According to the company's technology roadmap, it targets to achieve this by Q2/2024.
Solar cell equipment supplier Maxwell's VP, Overseas Sales, Peter Wolf chose to talk about his company's high throughput and low CapEx production equipment solutions for HJT.
Maxwell says that in 2024, it expects at least 20 W increase in the power of HJT mass-produced modules as the power of the 210×66 version module will be increased from 710 W to 730 W and those using electroplating technology will reach 745 W. This improvement will be a result of the manufacturer adopting a new texturing additive, CVD process and optimized equipment while also adopting no busbar module stringer technology.
With silver accounting for a large chunk of its cost, Maxwell said it targets to lower its consumption by bringing down the use of silver-coated copper to 35% in mid-2024 and 30% in late-2024, from 40% in late-2023.
Wolf shared that the manufacturer is also exploring going silver-free. The company is currently running a pilot test line with copper plating which it expects to go into mass production by 2025-26.
He sees impressive prospects for HJT in the future as the basic cell structure for next-generation technologies like perovskite.
HJT cell and module producer Winhitech's Product Director Guoqing Chen delved into the industrialization of efficient HJT technology during his presentation.
Its HJT cell efficiency in the lab has reached 26%, while that of mainstream cell in mass production has gone up to 25.7%. The management is working on reducing costs while increasing efficiency and reliability to promote the industrialization of HJT technology.
It has adopted the 110 µm wafer in industrial use for HJT cells compared to the 120 µm mainstream thickness. The company sees weak adhesive performance, weak anti-UV performance and sensitivity to moisture pose reliability challenges to the industrial prospects.
Winhitech says it has worked on these challenges using an adjusted film formula and light conversion film. It continues to assess high water-resistant silicone and butyl rubber as 2 solutions to deal with HJT's sensitivity to moisture.
Chen said the company continues to explore silver-coated copper, copper plating and 0BB configuration to further boost industrial prospects of this technology.
Established in December 2021, Winhitech calls itself an HJT-oriented new energy company that also offers TOPCon and PERC module products. Currently, its solar cell and module production capacity stands at 3 GW and 5 GW, targeted to be expanded to 30 GW and 15 GW by 2026, respectively.
Chen said that the company plans to enter the HBC domain as early as 2024 and into HJT-perovskite tandem by 2025 as per its technology roadmap.
R&D Director of PV Product at Cybrid, Carl Wang shared a breakthrough encapsulation solution to mitigate the UV-absorption losses for HJT cells. The company's UV conversion film RayBo converts UV light into visible light using a light conversion agent that's blended in POE/EPE/EVA encapsulant.
Wang said the RayBo completely absorbs UV light and releases visible light with a quantum transition rate of over 96.5%. Explaining why this kind of a UV conversion film works for HJT cells, he said it protects the cells from UV radiation, which can otherwise break the Si-H bond in a microcrystalline structure, thus reducing module output.
With UV conversion, Wang said module output for a 600 W module, for instance, can increase by around 1.5% or 10 W to 15 W.
While the best way to use the UV conversion film is to apply it on both the front and rear sides, it will increase the cost. Hence, the more cost-effective option, shared Wang, will be to use it on the front side with a transparent film on the rear.
The UV conversion film technology was invented by Dr. Onouchi Hisanari in 2013 and patented by Japanese electronics company Nitto Denko that later sold it to CHOSHU. Wang said Cybrid started developing RayBo using EVA and POE and now produces it commercially under the CHOSHU license since 2023.
Cybrid expects to report more than 5 GW of RayBo shipments in 2023 to leading HJT producers globally.
The Manager of Overseas Marketing/Sales for PV ribbon producer YourBest, Qin Yuchen discussed the application of 0BB interconnection technology in HJT PV modules.
The busbar usage has evolved from 5 BB to now 16 multi-busbar (MBB). The number of lines increases as busbars become smaller since smaller busbars mean less shadow and less use of silver paste. Nonetheless, smaller the busbar, the higher the resistance value.
However, Yuchen said his company offers zero busbar (ZBB) interconnection for HJT technology, and called it an upgrade to SMBB. Yuchen said a ZBB configuration brings down HJT's reliance on silver paste while ensuring higher light distribution.
He explained, "Earlier, the diameter of ribbon ranged between 0.29 mm to 0.4 mm but ZBB is much smaller with a diameter of around 0.2 mm. The less sunlight shadow, the higher the average of currency distribution."
TaiyangNews Head of Technology Shravan Chunduri had some rapid-fire questions for Head of Technology of the German research institute Forschungszentrum Jülich, Dr. Kaining Ding regarding HJT's potential with TOPCon being the new standard now.
Responding to Chunduri's query about how TOPCon has taken the lead over HJT when it comes to replacing PERC as the mainstream technology, despite the fact that till sometime back equal bets were placed on both, Ding argued that it is still too early to judge if HJT has made it or not.
He explained that while TOPCon scores over HJT in terms of cost, it is still a continuation of the same line of technology as BSF and PERC. But it is HJT that, as a new innovative technology, is doing pretty well on the field and is still evolving.
In fact, it is already a well-established technology, stressed Ding. At the same time, the industry players are working on further cost reduction and efficiency improvement. It remains to be seen how fast and how wide the gap between HJT and TOPCon can grow.
The bottleneck, of course, is the OpEx, which Ding said can be lowered by bringing down the use of indium and silver where work is already ongoing.
As Youru Tan of Bloomberg New Energy Finance (BNEF) pointed out in his presentation on day 1 of TaiyangNews High Efficiency Solar Technologies Conference, HJT is set to grow extensively outside China. It is because Chinese players already have an upper hand over TOPCon both in terms of technology and production capacity. Hence, HJT with its technical prowess is a suitable contender.
Ding signed off saying that he expects to see HJT as a mainstream PV technology over the next 3 years, while being used in tandem configuration for commercial use as well.
TaiyangNews High Efficiency Solar Technologies Conference will continue the discussion on December 19, 2023, with another round of talk about TOPCon technology. Our annual flagship event will end on December 20, 2023, with a day dedicated to back contact (XBC) and next-generation technologies. Register free for both the days here.