From pv journal 03/23
IBC photo voltaic cells had been conceived within the Nineteen Seventies and the thought behind them is straightforward: Transfer all contacts, metallization, and different internal workings of the cell to the rear facet, leaving the entrance, energetic layer unobstructed and open to extra daylight.
That method ensures IBC, and different back-contact sort gadgets, can push nearer to the sensible restrict for single-junction silicon cell conversion effectivity than different cell architectures. That purpose has stored them in focus for researchers, with most of the highest in-lab efficiencies coming from back-contact buildings.
Processing back-contact cells at scale, nevertheless, has confirmed troublesome and costly. The ensuing lack of adoption means comparisons with mainstream approaches are troublesome. “As the dimensions of again contact is small and it’s principally utilized in distributed-generation initiatives that pursue higher look, it has the next premium,” says Corrine Lin, chief analyst at renewables market intelligence firm InfoLink. “Based mostly on the product pricing of present producers, there’s normally a premium of $0.01/W, and even larger, in contrast with PERC [passivated-emitter, rear contact solar]. Nevertheless, there’s no clear premium index because of smaller buying and selling volumes and totally different goal markets.”
Most massive producers took an easier route to spice up effectivity, however with more cost effective avenues approaching exhaustion – and researchers at Germany’s Institute for Photo voltaic Vitality Analysis Hamelin final yr calculating back-contact gadgets might hit 29.1% effectivity – renewed makes an attempt to commercialize back-contact cells are afoot.
US firm SunPower Company manufactured IBC cells for greater than 20 years. Its merchandise have been significantly profitable within the residential market, the place the aesthetic look and superior effectivity and reliability is extremely valued, leading to a worth premium. In 2020, SunPower separated its manufacturing enterprise to type a brand new firm, Maxeon Photo voltaic Applied sciences, which continues to fabricate IBC merchandise below the SunPower and Maxeon manufacturers.
Doug Rose, vice chairman for know-how technique at Maxeon, explains the again contact construction allows the complete optimization of the entrance floor, maximizing gentle into the cell and minimizing recombination, as a substitute of additionally having to optimize for steel protection and lateral conduction to the steel fingers. On the rear facet, the IBC gives the chance for thicker steel, leading to decrease sequence resistance.
Rose provides that, alongside effectivity, superior reliability can be a spotlight for Maxeon, and having a premium product permits it to make design and supplies selections leading to reliability that’s higher than customary – it provides a product guarantee of as much as 40 years in some markets.
A key benefit of Maxeon’s IBC merchandise is that they’ve a singular, non-damaging reverse-bias conduct. This prevents hot-spots – which might trigger injury to cells and modules – even in partial shade with module diodes which have failed. “We consider this gives further worth and differentiation and we now have put a number of effort into extending the benefit on this space in our coming era.” Rose additional explains that the power to do that is one other inherent benefit of again contact know-how, although not current in all again contact architectures.
State of play
There are excessive hopes for back-contact photo voltaic. Radovan Kopecek, co-founder and director of German institute the Worldwide Photo voltaic Vitality Analysis Heart (ISC) Konstanz, advised pv journal in November, IBC modules might overtake TOPCon (tunnel-oxide, passivated contact) merchandise by 2028 and make up half of the market in 2030. Different market observers are much less bullish however agree that again contact applied sciences will doubtless see progress over the following 5 years.
“Step-by-step enhancements of producing processes and efficiencies are resulting in a gradual price discount for a lot of the back-contact applied sciences,” says Karl Melkonyan, senior analysis analyst at enterprise intelligence firm S&P World Commodity Insights. “A major price discount, nevertheless, would require extra time to completely develop. This may very well be appreciable discount in silver consumption; or whole alternative with copper or aluminum; or additional enhancements to soldering and cell interconnection processes, and different enhancements in effectivity, yield, and throughput.”
S&P World forecasts back-contact photo voltaic might attain 15% market share over the following 5 years. InfoLink expects progress to round 5% over the following two years to 3 years however little after that. “For the long run, its market share isn’t prone to attain the dimensions of PERC or TOPCon because of its complicated course of and better manufacturing prices,” says InfoLink’s Lin. “Though there’s nonetheless demand for back-contact – owing to its excessive effectivity and higher look – its market share isn’t prone to attain 10%.”
Maxeon has been pursuing such manufacturing course of enhancements. “Maxeon has a very proprietary course of with an amazing variety of patents defending the method,” says David Smith, a scientist at Maxeon’s California R&D hub. “Processes that we now have in pilot manufacturing at present use way more mainstream tools, so we are able to journey the coat tails of the TOPCon business. We use these large-scale, high-throughput instruments as a lot as potential and our new era makes use of the next fraction of these than ever.”
Saving and scaling
Maxeon, nevertheless, continues to be targeted on prospects who can pay a premium for efficiency and aesthetics, and says it’ll proceed to concentrate on its differentiated merchandise, even when extra mainstream IBC applied sciences begin to emerge.
ISC Konstanz believes the associated fee reductions wanted to again its bullish IBC expectations could be met. The analysis middle has developed “Zebra” IBC cells that are in the marketplace through manufacturing companions in Europe and Asia, and continues to drive down manufacturing price and lift effectivity.
“Our goal is to be, from the associated fee construction perspective, as shut as potential to straightforward know-how,” says Joris Libal, ISC’s venture supervisor for know-how switch. “We wish to begin with low-cost processes, straight from the toolbox, and get to excessive efficiencies.”
Valentin Mihailetchi, group chief of n-type [negatively-doped] cell R&D at ISC Konstanz, goes on to clarify Zebra cells are made utilizing standard processes together with tube diffusion, display printed metallization, plasma enchaced chemical vapor deposition, and laser ablation, including, “It’s about utilizing processes which can be already established, simply in a barely totally different approach.” That method might carry wider advantages as back-contact structure could be mixed with passivating contacts and different cell designs, providing one other path to mass manufacturing.
Other than the processing prices, IBC cells require silver contacts for each polarities. “In contrast with p-type [positively-doped] PERC, there’s perhaps 5% extra price for the wafer and a slight distinction for tools depreciation as a result of there’s just a little bit extra tools in comparison with PERC or TOPCon,” says Libal. “The primary distinction is the steel price.”
With much less have to make its rear-side fingers as skinny as potential in back-contact cells, although, ISC Konstanz is utilizing copper paste as a substitute of silver in its screen-printing course of. Standard producers, against this, have to make extra progress on copper-plating processes to cut back silver content material.
Whereas ISC Konstanz’s IBC cells nonetheless require some silver for the contacts – the copper can’t be in direct contact with the silicon – Libal says silver consumption could be decreased under 5 mg/W of cell era capability. That could be a fraction of the quantity utilized in PERC and TOPCon cells and would assist ease business considerations about silver provide.
The analysis institute is transferring forward with its copper display printing course of and says it has achieved good ends in accelerated testing up to now. “The Zebra IBC cell with copper metallization can be a breakthrough that can finally carry the price of IBC down under PERC, with the effectivity nonetheless properly above,” says Libal. “When these key parameters of price and efficiency are met, that’s when this can actually fly.”
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