Roadmap: Bifacial solar cells a key focus for Applied Materials

Rather than the previously expected technology buy cycle occurring ahead of a new wave of capacity expansions, 2014 will be noted for kick starting both cycles simultaneously that are expected to gain further momentum over the next few years. 

Therefore it did not come as a surprise that once-leading OEM, Applied Materials wanted to catch-up with PV Tech regarding some of its technology developments and recent successes after an absence from such activities primarily since EU PVSEC in late 2013. 

With most the PV equipment suppliers having hunkered down in bunkers for the last few years, Applied Materials is also of the opinion that a recovery is underway. 

According to Jim Mullin, VP, GM Solar Products at Applied Materials, the PV market is expected to remain strong through 2018, driven by 15% or more annual growth rates, while PV manufacturers focus on increasing cell/module efficiencies at 10W per annum or more. 

Mullin noted that Applied Materials spent a lot of time and effort in 2014, discussing with many of the tier-one PV manufacturers about business drivers and their technology roadmaps. 

“One constant we have analysed is that the current [downstream] industry growth pretty much globally has been tied to project development IRRs [investor rate of return], and in most cases the IRR is very attractive and is difficult to get returns better than 12% in any other investment currently,” remarked Mullin. 

Indeed competition coupled to improving market conditions could lead to accelerating efficiency improvements, which would require greater spending on new equipment and faster adoption of new cell architectures such as PERC for P-type multicrystalline. 

However, Applied’s VP believes that other key forces are at play and again being driven by the downstream market on the upstream manufacturers. 

“Higher energy yields are driving the IRRs. Tier-one manufacturers are shifting their technology roadmaps to higher energy yield focus,” added Mullin. “Of course this primarily comes from higher cell efficiencies. The consistent feedback we have been given is that conventional module outputs are rising by around 10W per year and that is likely accelerating.” 

It has become increasingly obvious in 2014 that p-type multicrystalline solar cell producers, which dominate the PV market, are entering around a five-year period of upgrading lines and adding new capacity to migrate to a variety of PERC-based cell architectures as roadmaps push to maximise significant P-type investments. 

However, Applied’s Mullin believes p-type multicrystalline cell efficiency gains are both reaching their limits and as they do they become increasingly impacted by LID (light induced degradation).

“Cells efficiency gains are supporting modules at 260W plus this year but at 270W, this we believe represents the end of road for standard products, with cells peaking at around 18.5% conversion efficiencies. What we are seeing more and more is the shift the mono, notably first with Taiwan and Korean producers.”

Applied is betting that monocrystalline wafers in both p- and n-type configurations are to make a comeback as efficiencies are inherently higher than multicrystalline and are not impacted by LID. Higher carrier mobility lifetimes of mono also will play a part in the shift in wafer choice as well as the monocrystalline wafer producers' efforts over recent years to significantly close the gap on production costs with multicrystalline wafers. 

Indeed, according to Mullin and PV Tech’s own coverage, monocrystalline wafer costs are set for further significant cost reduction over the next three years. In essence an inflection point for monocrystalline wafers is approaching. Mullin said Applied expects monocrystalline wafers to account for over 50% of the market by the end of 2018. Currently, multicrystalline dominates with over 65% of the market. 

Within that expected shift, which contrasts with views of PV market analysts such as Finlay Colville, PV manufacturers will also increasingly switch production to n-type technology as higher efficiencies become the key driver of the industry, driven by LCOE reduction requirements in key end commercial and residential markets. 

Justification for sighting the migration to n-type monocrystalline other than the technical benefits is that the higher efficiency and quality of n-type monocrystalline leads to a price premium, something that will increasingly become important to an otherwise commodity product. 

Applied’s recent successes 

In the wake of the transition to n-type monocrystalline wafer/cells, Mullin cited recent successes the company has had with its Solion ion implant tools, notably its next-generation XP version that was launched at EU PVSEC in 2013. 

According to Mullin, Applied is focusing its Solion XP implanter at n-type monocrystalline bifacial cells, having recently secured an order from Mission Solar as part of its next 100MW line expansion in Texas. Mullin said that Mission Solar has purchased two Solion XP implanters, which also replace the need for diffusion systems in the new turn-key line. 

The largest merchant cell producer, Neo Solar Power (NSP) had also adopted the tool for n-type bifacial cell production, noting that NSP was able to extract a premium price for those cells in the market. 

Applied had also won implant orders for n-type bifacial cell production from a customer in Korea, which will use the Soilon XP implanter in a new 200MW cell expansion, while further orders form Korean PV manufacturers were on the cards. 

Momentum for adopting Applied’s Soilon XP ion implanter in n-type monocrystalline bifacial cells was growing, leading to an expected 500MW of capacity coming online by mid-year 2015, according to Mullin. 

That trend was set to continue with a conservative estimate by Mullin that around 1GW of production would be operational in 2016. 

Supporting claims by Applied that ion implant is gaining traction come from the likes of Yingli Green and rival implanter equipment supplier, Kingstone Semiconductor, a majority-owned subsidiary of Amtech Systems, which had previously developed its IonSolar system. 

In a PV Tech exclusive at the SPI event in Las Vegas late last year, Brian Grenko, VP technology at Yingli Green Energy Americas highlighted at the company’s annual analyst day event that from the beginning in 2014, Yingli Green had incorporated ion implantation into its n-type monocrystalline ‘Panda’ cell architecture. 

The fact that ion implantation is even being considered for volume production applications is a testament to the ongoing of the development work of the tools for PV applications. 

Steve Krause, senior director, Implant Solar Products at Applied Materials ran through with PV Tech the critical developments that have established the Solion XP as a tool for PV cell production. 

This included the tool's unique precision scanning and 2D hard mask capability that enables the XP tool to be future-proof to a number of future advanced cells architectures such as n-PERT n-PERL and HJT and IBC cells all dependent on n-type monocrystalline wafers. 

Krause also reiterated much of the XP’s abilities as that given by Wessley Skinner, global product manager at Applied Materials in a PV Tech video shot during EU PVSEC in 2013. 

However, the confidence of Applied in the XP’s ability has increased since then with Krause highlighting the tools capabilities of enabling advanced process technologies to reach greater than 22% efficiencies with a 50% lower cost per wafer than the initial Solion tool. 

In production environments the ability of providing 3,000WPH throughput coupled with highly accurate dopant depth, dose and placement of Phosphorous and Boron results in improved cell efficiency (greater than 0.6% gain) and yield as well as narrow efficiency binning, creating both a robust manufacturing technology but one that holds an ROI of around one year. 

“The higher throughput for a lower cost per watt is really resonating with customers and is behind the momentum of the tool over the last 20-months,” said Krause. “Crucially the Solion XP has the extendibility to next generation solar cells such as n-type PERL and IBC cells with its patterning capabilities, which extends cell efficiencies to around 23%.”

PV manufacturers that had previously baulked at ion implantation as a mainstream manufacturing technology would seem to be thinking twice as the technology has rapidly matured in recent years.