XBC & Next Gen: High Efficiency Solar Technologies Conference Day 4

Tremendous Scope For Back-Contact Technology; Tandem Holds Potential But GW-Scale Mass Production Still A Long Way Off

XBC & Next Gen: High Efficiency Solar Technologies Conference Day 4

The executive panel moderated by Shravan Chunduri of TaiyangNews had FuturaSun’s Gianluca Coletti, GCL Perovskite’s Fan Bin and Leadmicro’s Dr. Wei-Min Li discussing pathways to transition from pure silicon to tandem. (Photo Credit: TaiyangNews)

  • The last and the final day of the 4-day TaiyangNews Virtual Conference on High Efficiency Solar Technologies explored next-generation technologies 
  • Back-contact holds immense promise especially as tier 1 manufacturers explore it  
  • Future of the solar PV industry is likely to see the coexistence of various technologies 

Having discussed the latest in the world of TOPCon and HJT on 3 days of the TaiyangNews High Efficiency Solar Technologies Virtual Conference, day 4 of our annual flagship event focused on back-contact (XBC) and next-generation technologies.  

In his keynote address, FuturaSun Holding CTO Gianluca Coletti discussed key innovations in next-generation PV with cost reduction and efficiency improvement as the main motivation for the industry to explore newer avenues beyond current incumbent PERC. 

Coletti sees the monochromatic PV technology era (dominated by Al-BSF earlier and later by PERC) coming to an end, and the PV industry moving towards multicolor PV technology era starting from 2024 with multiple mainstream technologies including TOPCon, HJT and XBC. 


FuturaSun’s Gianluca Coletti sees monochromatic PV technology era coming to an end and the PV industry moving towards multicolor PV technology starting from 2024. (Photo Credit: TaiyangNews)

This diversity will be needed since there are more PV applications now and the industry is reaching the practical limit of single junction technology. It will become overly costly to maintain. 

While the industry is in extreme control and understanding of manufacturing and supply chain, as it moves towards a multi-TW era, there are challenges that need to be faced head on. Coletti identifies these challenges as lowering silver consumption by at least 4 times and reducing dependence on indium and bismuth. This can be achieved through higher efficiency with better use of material and going the tandem way for low current and high voltage promise. 

The main tandem configurations are 2-terminal cell based, which looks like a typical silicon module, and the 4-terminal module that resembles a typical thin-film module top and silicon module at the bottom. However, for tandem to become the norm, it will need to maintain an efficiency increase beyond the practical single junction technology limit. Coletti stressed on including bifaciality in tandem as well to better use the bottom device. 

Among the challenges tandem technology faces, Coletti believes the super large area efficiency still needs to be demonstrated in real world conditions, outside the lab. Similarly, the lower OpEx of perovskite also needs to be proved, along with its reliability and stability over a period of 25 years, which requires more research. 

He added that there is still no clear winner as to which technology is the best out of the cell-based and module-based tandem since both have their challenges and opportunities. Their growth will also depend on various applications, which means customization will also become important going forward. 


LONGi’s Dr. Heng Sun said BC integrated solar cell technologies, namely HPBC, TBC and HBC, help deliver higher cell efficiencies, as this NREL slide from his presentation shows. (Photo Credit: TaiyangNews)

LONGi’s R&D Chief Engineer Dr. Heng Sun shared the progress of the company’s high efficiency hybrid passivated back contact (HPBC) solar cell R&D and its industrial application. 

Conversion efficiency and LCOE reduction are primary objectives for any solar technology, said Sun, both of which are offered by BC. While the theoretical cell efficiency limit of TOPCon is 28.7%, and HJT 28.5%, that of BC is higher at 29.1%. 

LONGi recently announced achieving 27.09% new efficiency world record for crystalline silicon HJT back contact (HBC) solar cells (see New ‘World Record’ Efficiency For HBC Solar Cells). 

Calling HPBC a redefined technology, Sun said LONGi’s HPBC technology has no finger patterns, giving it an aesthetic all-black look. It uses passivation layers on both the front and rear sides. It benefits from the cost-effectiveness and process simplification of c-Si solar cells, and the zero front-shading loss and aesthetics of IBC. 

Working on the HPBC design concept since 2017, LONGi achieved over 25.8% average cell efficiency in mass production and aims to scale it up to 26.5% by 2025. LONGi’s HPBC annual production capacity stands at 30 GW at 2023-end, having increased it from 20 GW in early 2023. 


AIKO Solar’s MA Jiayu listed features that make its ABC technology stand apart from other technologies, especially making it the choice for aesthetic PV display. (Photo Credit: TaiyangNews)

Aiko Solar’s Product Manager MA Jiayu presented the solar cell and module maker’s All Back Contact (ABC) technology that combines stunning aesthetics with high efficiency.  

Based on n-type solar cell, the ABC technology of AIKO uses grid lines, electrodes, and passivating contacts at the back of the cell instead of the front, which is what differentiates it from other technologies. 

Through the use of a self-owned patent design for all-back electrode technology, Jiayu said the company is able to reduce the heating loss of electrode resistance by 60% compared to traditional technologies. With no grid lines on the front, AIKO targets its aesthetic looking modules for the residential and commercial & industrial (C&I) applications. It recently launched the Stellar series for the utility market with up to 23.9% efficiency and 645 W output (see AIKO Solar Launches Its 1st Bifacial Back-Contact Cell Modules). 

There are 2 passivation layers to the ABC cell, one each for the front and the rear. The passivation layer at the back is a BC+Bi-pole passivation. It also uses a patented silver- (Ag) free metallization technology for the cell process and all metals used are low-cost. Going silver-free brings down its cost and also improves reliability, explained Jiayu, since it requires high temperature.  

Other features of the AIKO cell are micro-crack resistance, -0.26% temperature coefficient and hot spot temperature of 90-110 °C. In comparison, TOPCon and PERC have a hot spot temperature of 140-150°C and 150-160°C, respectively, she added. 

Currently, AIKO is on top of the TaiyangNews Top Modules Listing with an industry leading 24% efficiency (see Top Solar Modules Listing—November 2023). However, Jiayu said since the theoretical mass production efficiency of BC can exceed 27%, AIKO believes the mainstream of n-type solar cells will be the BC. 

AIKO’s current annual solar cell production capacity stands at 61 GW and 25 GW for ABC modules. It is present in the entire value chain, from polysilicon to module and system solutions. Jiayu said this provides the manufacturer with a stable supply chain and it can control quality every step of the way. 


Dr. Radovan Kopecek of ISC Konstanz called XBC the best solution for the future of PV market as mainstream companies invest in it. (Photo Credit: TaiyangNews)

The Managing Director of Advanced Cell Concepts and Member of the ISC Konstanz Executive Committee Dr. Radovan Kopecek delved into the future of Cu screen printed bifacial XBC for utility-scale. It targets to achieve cost-competitive bifacial IBC technology for vertically integrated GW-scale PV production value chain for Europe, to expand from rooftop to utility-scale PV under the EU funded IBC4EU project. 

Under this project, ISC has developed the ZEBRA cell using screen printing technology from Copprint. It has now partnered with FuturaSun to bring ISC Zebra into production. 

Reflecting on the growth of the n-type technology over the last 18 years since the ISC started working on it, Kopecek argued that XBC will go to the next level as TOPCon is completely standardized. He believes XBC is the best solution for the future of the PV market as more and more companies realize its potential. 

As more and more tier I manufacturers like LONGi, AIKO and FuturaSun explore XBC, Kopecek forecasts large-scale migration towards back contacts by 2030 or even slightly earlier. 

At the moment, while the industry mainly pursues copper plating as an alternative to silver-based metallization, ISC targets to go towards screen printing with Copprint whose copper paste doesn’t oxidize. 

Kopecek believes XBC will come to the utility market from 2028, for which it needs to go to copper plating and solve polysilicon boron diffusion issues.  


Von Ardenne’s Dr. Sebastian Gatz believes PVD deposition offers the most stable and reproducible process environment for tandem PV technology. (Photo Credit: TaiyangNews)

Vacuum coating systems supplier Von Ardenne’s Vice President Dr. Sebastian Gatz shared his views on PVD technology as the answer to the challenges for IBC, TOPCon, HJT and tandem in GW-scale production. The company says it has supplied more than 72 GW of PVD equipment for PV since its inception. 

A PVD coatings supplier for various PV technologies at various stages, Von Ardenne supplies plasma technology with rotatable dual magnetron sputtering for TOPCon, HJT, IBC and tandem, along with evaporation technology with linear co-/evaporation unit for perovskite.  

Gatz shared that while TOPCon and HJT are in the market penetration phase with capacities way above 5 GW per customer, IBC technologies are entering multi-GW production, especially next year. He, however, said that tandem still remains at the R&D and pilot lines. Gatz expects tandem to start GW-level production in 2025. 

For TOPCon PVD, the Von Ardenne equipment offers the same efficiency level as LPCVD, added Gatz, who sees huge cost savings potential as well. For copper plating for HJT and IBC, PVD metal layers work best as seed layers. 

Talking about the challenges in bringing tandem solar cells to GW production in terms of improving stability and cost-effective process flow, Gatz believes the vacuum processes or a combination with solution-based processes are considered as the right counter-approach. He believes PVD deposition is the solution for tandem coating for high-volume manufacturing as it offers a stable and reproducible process environment. 


GCL Perovskite’s Fan Bin shared the company’s technical roadmap under which it is set to start work on a GW-scale tandem module fab in China. (Photo Credit: TaiyangNews)

Speaking of tandem technology, GCL Perovskite’s Chairman of the Board Fan Bin talked about perovskite-based tandem solar PV modules. Founded in 2010 as Xiamen Weihua as an organic PV (OPV) company, it switched to perovskite in 2014 with a 10 MW R&D line. It was eventually acquired by the GCL Group in 2016 and branded as GCL Perovskite. 

Bin said the company today operates a 2m x 1m perovskite module pilot line with 100 MW capacity, and has achieved 18% efficiency for single-junction standard-size perovskite solar module. It now plans to expand to GW-scale production to produce crystalline silicon and perovskite tandem modules for an eventual 2 GW capacity to be realized in phases as the world’s 1st GW-scale mass production perovskite module fab, in China. In 2024, GCL Perovskite targets to achieve a tandem efficiency of 26% for the 2m x 1m module, exceeding 27% in 2025 on a 2.4m x 1.2m size. 

Its production process differs from other manufacturers though, as Bin explained, GCL uses a module-level tandem structure, meaning it crystalizes perovskite on a flat glass surface instead of directly on the c-Si surface that can hamper the uniformity of the perovskite film and crystal quality. 

The use of lead in perovskite is questioned, but Bin argued that the quantity is much less than silicon as each perovskite module uses 2g of lead compared to 16 to 18g in crystalline silicon. 

Apart from the ease of availability of perovskite and its high efficiency potential, Bin pointed to its low carbon footprint and ease of manufacturing since it can be produced at any location within 45 minutes for end-to-end production. The c-Si manufacturing needs to go through 4 factories and requires a minimum of 3 days for the modules to come out. This also brings down costs. 


Solamet’s Kaien Chang sees high-efficiency tandem cell as the next-generation PV technology after n-TOPCon/HJT. He said efficiency increase & cost reduction will depend on innovative screen-printing metallization. (Photo Credit: TaiyangNews)

Solamet’s Vice President of Technology-Overseas, Kaien Chang shared his company’s low-temperature paste development for next-generation HJT/perovskite tandem cells. 

He believes the high-efficiency tandem cell is expected to be the next-generation PV technology after n-TOPCon/HJT. Its efficiency improvement and cost reduction will depend on innovations in screen printing metallization. 

Sharing the Chinese company’s roadmap for the development of low-temperature metallization paste, Chang said Solamet is now offering a paste for HJT and also focusing on silver-coated copper pastes. While the market uses around 50% silver content for HJT applications, Solamet claims to have lowered its content to 35% for the silver-coated copper paste with improved contact and conductivity. It plans to soon launch the same into the market. 

The manufacturer is also working on a low-temperature paste at under 130 °C for high-efficiency thin-film perovskite solar cells, including tandem. 


Leadmicro’s Dr. Wei-Min Li said ALD has good potential for perovskite cells & its batch ALD equipment has been implemented in a pilot line for tandem cells. (Photo Credit: TaiyangNews)

Discussing the progress in developing production equipment for perovskite solar cells, Leadmicro CTO Dr. Wei-Min Li said he believes ALD shows good potential for perovskite cells, which it has sold 500 GW of capacity globally. 

The company’s batch ALD equipment has been implemented in a pilot line for tandem cell applications with the newest record of 28.6% for 258.15 cm² while domestic single-junction cell efficiency has reached 32.44% on 1 cm². 

Most of Leadmicro’s work is focused on the batch type of ALD process, which is currently mostly used in PERC and TOPCon. It operates both R&D as well as production level work for perovskite in this space, claiming to offer a complete pilot line for perovskite solar cell production.  


Copprint’s Ofer Shochet said the company’s low-cost conductive paste for the PV industry is based on its copper screen printing technology that does not oxidize, but offers the same conductivity as top silver pastes. (Photo Credit: TaiyangNews)

As silver gets more expensive, the industry is looking at copper as a viable solution for PV cells. Israel-based screen printable copper paste supplier Copprint CEO and Co-Founder Ofer Shochet said his company offers conductive low-cost copper pastes for PV metallization. 

Referring to the growing demand for silver from the PV industry, Shochet said PERC uses 10 mg/W silver while TOPCon and HJT use 13 mg/W and 22 mg/W, respectively. The trend to go towards a higher efficiency cell exists; hence the demand for this expensive metal will go up too, along with prices. 

The current price for silver/kg is at around $800, while copper costs around $9/kg. The latter has almost the same conductivity and is 1,000 times more abundant than silver, and 10 times less toxic. 

Copprint’s patented chemical rapid sintering ensures there is no oxidation or corrosion, explained Shochet. It uses standard equipment ‘under air’ process with high throughput and low CapEx. The sintering process on HJT cells, for instance, takes about 5 to 12 seconds. 

It is currently providing this screen-printing copper paste solution for ISC Konstanz’ IBC Zebra solar cells that’s now ready for production. FuturaSun plans to adopt this technology, starting in 2024. 

Copprint is charging $708/kg and $400/kg for 500 kg of its pastes. Vis-à-vis silver that’s very volatile, Shochet said his company is committing on future pricing for over 2 years. 

Executive Panel 

Moderated by TaiyangNews Head of Technology Shravan Chunduri, the executive panel discussion revolved around pathways to transition from pure silicon to tandems. 

Sharing the learnings from its pilot line for the last 10 years, GCL Perovskite’s Fan Bin said perovskite works better on glass than on a surface of textured silicon wafers. He called it the right strategy to move forward in this direction. It is important since that way the company does not need to compete with silicon modules directly which will be very tough. “Directly go to high efficiency. Better way to survive,” he added. 

FuturaSun’s Gianluca Coletti placed his bets on the BC technology that gives a highly efficient and good-looking module. Since the BC is applied on the back of the cell, manufacturers have one less problem to worry about, and that’s interconnection. However, even for tandem, bifaciality needs to work. He said tandem is quite promising but till it can prove its reliability, the world should install as much PV as it can. 

Leadmicro’s Dr. Wei-Min Li said the need is to work on metallization for BC to make it work better and efficiently. As for perovskite tandem, he believes currently the main challenge, in the absence of tools, is to work on larger substrates to prove its mainstream potential. 

The TaiyangNews High Efficiency Solar Technologies conference explored TOPCon on day 1, HJT on day 2 and continued the discussion on TOPCon on day 3 of our annual flagship event. 

About The Author

Anu Bhambhani

Senior News Editor: Anu Bhambhani is the Senior News Editor of TaiyangNews. --Email : [email protected] --

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