The 24th European Photovoltaic Solar Energy Conference and Exhibition (PVSEC) gave Linde Gases the opportunity to promote sustainability, focusing on the benefits of using fluorine (F2) in place of nitrogen trifluoride (NF3); gasworld spoke exclusively to two Linde professionals who attended the event.

It’s just over a year since gasworld reported that Linde Gases had devised a solution to reduce environmental damage during the production of LCD’s and solar panels.

The company pioneered the idea of replacing NF3 (used as a cleaning gas in the PV manufacturing process) with pure F2, which has zero Global Warming Potential (GWP).

In June of this year, Malibu - a joint venture between energy company E.ON, and Schuco, a major worldwide provider of building envelope systems – launched the world’s first thin film solar module factory, using on-site generated F2 made with Linde’s patented technology.

This major contract pushed Linde’s F2 technology into the spotlight, proving its viability as a green alternative to NF3. Linde Gases is now keen to build on this attention, encouraging others to switch from grid parity to green parity, not just in terms of F2 technology, but on a wider scale, and PVSEC was the perfect opportunity to educate people on the company’s green initiatives as a whole.

“PVSEC was a four-day show, probably the biggest PV technical exhibition and conference in the world and all the gas companies were there,” Steve Pilgrim, Global Marketing Manager for Linde Electronics told gasworld.

“We were promoting sustainability; we had a seminar on the Thursday where we pulled together influential people within the industry – people like ourselves who supply a particular technology that solar cell manufacturers need.”

“There was a broader discussion on all of the pieces of the gas puzzle that could be fine tuned to reduce the CO2 footprint. Fluorine is a large opportunity, but also, if you move things to on-site generation and change the ways you run your supply chain, you can significantly reduce the CO2 across the supply chain.”

Paul Stockman, Linde Gases’ Head of F2 for the PV market also attended the event; his focus was on thin film application, and new technology applications for fluorine. He told gasworld, “We saw a definite acceleration in the adoption of interest among major thin film manufacturers.”

“Last year, the event was held in Valencia. At that time we were still in the phase where the economy hadn’t quite shown all of its cards, and people were quite bullish, looking at over 50 percent growth per year in PV.”

“This year was a much more sober year, but at the same time, with a year of better analysis, people are looking at a steady 20 to 30 percent growth. The event showed a steady progress on both efficiency and cost, and people are really focusing on value right now, rather than just a little bit of undue exuberance I think that we saw last year.”

“So there was a great deal of interest in technologies that could increase the level of automation, standardisation, and at the same time help reduce costs and cost of ownership.”

A move towards sustainability
Fluorine’s role in thin film processes is as the chamber cleaning gas. When manufacturing products like flat screen LCDs, thin films are created on glass substrates in large vacuums; any sort of particle contamination from one substrate to the next must be eliminated; therefore for every substrate, or every few substrates, the chamber must be cleaned.

Fluorine is an attractive alternative to sulphur hexafluoride (SF6) or NF3 for this process, not just because of its green qualities, but because it can greatly reduce costs.

“Fluorine is inherently less expensive to produce than NF3,” explains Stockman.

“In addition, it also has a tremendous through-put benefit for the customers; it’s chemically more active and requires less energy to complete the process, this means that the cleaning step, which can be anywhere from five to 20 percent in the manufacturing cycle, can be reduced by two to four times.”

“When you have very expensive equipment – tools that are costing in the order of five to 20 million dollars each – if you can increase the up time it is very beneficial, because it lowers the overall cost of operations.”

Aside from its use as a chamber cleaning gas, fluorine has great potential for other PV processes, such as crystalline manufacturing.

“One key technology that several equipment manufacturers have wanted to know more about was the transition of crystalline silicon from wet processing to dry processing,” Stockman explained.

“Dry processing using gas related processes instead of liquid related processes allows manufacturers to go to higher rates of automation with thinner wafers and reduced waste stream, and fluorine can be part of this in several different processes.”

The PVSEC show proved useful in gaining a general consensus of where manufacturers were at in terms of the adoption of fluorine into their processes.

Stockman commented, “The equipment manufacturers that approached us, in considering going from wet to dry processes, have told us that NF3 is just not an option for them because of the environmental concerns. They don’t want to start out with a gas that has such a high global warming risk.”

The future
So what does the future hold in terms of Linde’s goals for a greener industry? According to Stockman, we will begin to see further adoption of fluorine as a chamber cleaning gas for thin film processes in 2010.

He commented, “You will see this happening in two stages; first will be a follow-on from the type of work being seen with Malibu, which is showing that for certain platforms, there is a commercial advantage of using fluorine. Then will come a more general replacement of greenhouse gases with things that are more benign for the environment.”

Pilgrim echoed this view, believing that the implementation of fluorine as a cleaning gas is a ‘quick win’, but noting also that other areas of the process will come into focus as well, to see where CO2 output can be reduced.

He said, “Every step of the manufacturing chain should really be looked at to see if you can make it greener.”

“You can take a big chunk out of the quantity of CO2 created in making a solar cell, just by moving from NF3 to F2, but as a material supplier, we can then look at other pieces of the supply chain and characterise that in terms of CO2 equivalence, and see how many of those we can take out.”

Pilgrim mentioned the use of silane in thin film solar manufacturing, suggesting Linde will soon be addressing the supply chain of this widely used gas.

Stockman elaborated, “It’s a general progression we have for thin film growth - initially we’re supplying customers in small packages like cylinders, then we progress to supplying them in bulk packages like trailers and liquid supply, and eventually we will move to provide them with the most efficient method, which is on-site manufacturing.”

“We’re already doing this with fluorine for our largest customers, with hydrogen and nitrogen, and we can progress to do this with things like silane. At the very largest scale we can supply customers with inert gases and hydrogen on an even more economical scale, which is by shared pipeline.”

Pilgrim also touched on gas dopants, noting the benefits of precision blending on-site, rather than having hundreds or possibly thousands of dilute mixtures being delivered.

“For a large scale fab you could need up to 6000 cylinders if you brought them in a very dilute mixture, however we expect it be about 40 cylinders if you brought the concentrate and then blended it,” he commented.

Linde knows that for its customers, cost is paramount. Therefore, by finding cost cutting solutions which are also green solutions, they are steadily moving the industry towards a greener future.

The PV sector is expected to be one of the branches of the industrial gas tree which is most likely to blossom in the coming years, and the high quantity of gases used in the processes means the industrial gas companies have a duty to devise cleaner methods.

Pilgrim explains, “In semiconductor, the amount of gas it takes to makes a chip is very small, less than one percent of the overall bill of materials; in PV it could be 15 or 20 percent.”

He continued, “Although the industry hasn’t got as big yet, the growth potentials that have been talked about and what we’ve seen pre-downturn indicate that it’s a very interesting market.”

“I think we’re starting on a journey; we’ve seen a lot of activity around sustainability recently. The semiconductor industry has done a good job over the last few years, although they’ve had maybe 20 or 30 years to look at their sustainability and their greenness. The PV industry must quickly learn from these lessons and make sure it doesn’t get into bad habits.”