Weekend Learn: So simple as IBC

From pv journal 03/23

IBC photo voltaic cells have been conceived within the Nineteen Seventies and the thought behind them is easy: Transfer all contacts, metallization, and different inside workings of the cell to the rear facet, leaving the entrance, lively layer unobstructed and open to extra daylight.

That method ensures IBC, and different back-contact kind gadgets, can push nearer to the sensible restrict for single-junction silicon cell conversion effectivity than different cell architectures. That objective 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, nonetheless, has confirmed troublesome and costly. The ensuing lack of adoption means comparisons with mainstream approaches are troublesome. “As the size of again contact is small and it’s largely utilized in distributed-generation tasks that pursue higher look, it has a better premium,” says Corrine Lin, chief analyst at renewables market intelligence firm InfoLink. “Primarily based 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]. Nonetheless, there’s no clear premium index as a consequence of smaller buying and selling volumes and completely different goal markets.”

Most giant producers took a less complicated route to spice up effectivity, however with more cost effective avenues approaching exhaustion – and researchers at Germany’s Institute for Photo voltaic Power Analysis Hamelin final 12 months calculating back-contact gadgets may hit 29.1% effectivity – renewed makes an attempt to commercialize back-contact cells are afoot.

IBC benefit

US firm SunPower Company manufactured IBC cells for greater than 20 years. Its merchandise have been notably profitable within the residential market, the place the aesthetic look and superior effectivity and reliability is very valued, leading to a worth premium. In 2020, SunPower separated its manufacturing enterprise to kind 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 permits the total optimization of the entrance floor, maximizing gentle into the cell and minimizing recombination, as an alternative 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 collection resistance.

Rose provides that, alongside effectivity, superior reliability can also 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 normal – it presents 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 novel, non-damaging reverse-bias habits. This prevents hot-spots – which may trigger injury to cells and modules – even in partial shade with module diodes which have failed. “We imagine this gives further worth and differentiation and we have now put lots of effort into extending the benefit on this space in our coming technology.” Rose additional explains that the flexibility 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 Power Analysis Heart (ISC) Konstanz, informed pv journal in November, IBC modules may 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 possible see development over the subsequent 5 years.

“Step-by-step enhancements of producing processes and efficiencies are resulting in a gradual value discount for a lot of the back-contact applied sciences,” says Karl Melkonyan, senior analysis analyst at enterprise intelligence firm S&P International Commodity Insights. “A major value discount, nonetheless, would require extra time to totally develop. This may very well be appreciable discount in silver consumption; or whole substitute with copper or aluminum; or additional enhancements to soldering and cell interconnection processes, and different enhancements in effectivity, yield, and throughput.”

S&P International forecasts back-contact photo voltaic may attain 15% market share over the subsequent 5 years. InfoLink expects development to round 5% over the subsequent two years to 3 years however little after that. “For the long run, its market share is just not more likely to attain the size of PERC or TOPCon as a consequence of its advanced 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 is just not more likely to attain 10%.”

Maxeon has been pursuing such manufacturing course of enhancements. “Maxeon has a very proprietary course of with an incredible variety of patents defending the method,” says David Smith, a scientist at Maxeon’s California R&D hub. “Processes that we have now in pilot manufacturing right now use rather more mainstream gear, so we will journey the coat tails of the TOPCon trade. We use these large-scale, high-throughput instruments as a lot as doable and our new technology makes use of a better fraction of these than ever.”

Saving and scaling

Maxeon, nonetheless, remains to be targeted on clients who can pay a premium for efficiency and aesthetics, and says it’s going to proceed to give attention to its differentiated merchandise, even when extra mainstream IBC applied sciences begin to emerge.

ISC Konstanz believes the price reductions wanted to again its bullish IBC expectations may be met. The analysis middle has developed “Zebra” IBC cells that are available on the market through manufacturing companions in Europe and Asia, and continues to drive down manufacturing value and lift effectivity.

“Our goal is to be, from the price construction standpoint, as shut as doable to plain 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 typical processes together with tube diffusion, display screen printed metallization, plasma enchaced chemical vapor deposition, and laser ablation, including, “It’s about utilizing processes which are already established, simply in a barely completely different approach.” That method may convey wider advantages as back-contact structure may be mixed with passivating contacts and different cell designs, providing one other path to mass manufacturing.

Silver consumption

Apart from the processing prices, IBC cells require silver contacts for each polarities. “In contrast with p-type [positively-doped] PERC, there’s perhaps 5% extra value for the wafer and a slight distinction for gear depreciation as a result of there’s somewhat bit extra gear in comparison with PERC or TOPCon,” says Libal. “The primary distinction is the steel value.”

With much less must make its rear-side fingers as skinny as doable in back-contact cells, although, ISC Konstanz is utilizing copper paste as an alternative of silver in its screen-printing course of. Typical producers, in contrast, must make extra progress on copper-plating processes to scale 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 may be diminished under 5 mg/W of cell technology capability. That may be a fraction of the quantity utilized in PERC and TOPCon cells and would assist ease trade considerations about silver provide.

The analysis institute is shifting forward with its copper display screen printing course of and says it has achieved good leads to accelerated testing to date. “The Zebra IBC cell with copper metallization might be a breakthrough that can finally convey the price of IBC down under PERC, with the effectivity nonetheless nicely above,” says Libal. “When these key parameters of value and efficiency are met, that’s when it will actually fly.”