While the focus of much of the PV manufacturing community in recent years has been on achieving cost reductions, it appears that a major push towards efficiency improvements is underway. UNSWs Martin Green says that while it has been more than 30 years since he drew his first PERC diagram, things are starting to happen there finally.
How would you sum up where the PV industry is at the moment from a technology basis, of new technologies coming out onto the market and into production?
It seems to me a transition is taking place with many of the leading companies now switching from the standard back-surface field kind of processing approach to the passivated emitter rear cell (PERC).
Why do you feel PERC is gathering real momentum in production right now?
We got a big burst in performance when we went to the PERC because we could access voltages that previously we couldnt get with just an aluminum-surface field. Now there might be a 5% or 10% performance margin with the PERC, but I think that could grow.
We found a 20% performance margin in our laboratory cells once we got everything perfected. So I think the industry can look towards those kinds of advantages as they push harder and harder into the technology.
Monocrystalline PERC seemed to be the first stage of PERC rollout, but it seems the multicrystalline PERC is now being adopted pretty quickly into production. Is that also what you are seeing?
I was amazed at the recent Trina Solar result where it was able to achieve 20.8% conversion efficeincy with a multcrystalline silicon PERC cell. That is better than what we have been able to achieve in the laboratory, regardless of how many stops we pull out!
I guess the multicrystalline is improving so eventually it will be able to get pretty much the same performance as monocrystalline, so its been gaining on the monocrystalline. Mono has been pretty much stationary in terms of the performance you can get from it while the multi is improving year after year. So eventually the gap will get narrower and narrower.
I think that multicrystalline PERC will eventually achieve something like 25% efficiency on the cell level.
There are a number of production processes and pieces of production equipment that can be employed in PERC production. What is your take on what are the best solutions for PERC upgrades?
It seems that eventually everyone will come to a common opinion as to what the best technique is. It is very early days and it is probably going to take a while for everyone to work out on which is the one that should be concentrated. But I think that is the nature of the industry: The best solution gets identified and the whole industry zeros in on it eventually. With time I think it will become clear.
The plasma-assisted processes are the ones that have dominated for the antireflection coating (ARC) but I dont know whether that will happen for the rear dielectrics as well, as it could be something else.
With multicrystalline PERC application I understand there are considerably more technical challenges, particularly when it comes to preparing the wafer and texturing. Are you confident that these challenges can be overcome?
I think so. It is just a matter of someone finding a way that works well for texturing. The industry is of the nature now that the processes that become cheap are those that everyone adopts. It is not the unique solutions that drive the industry forward, its the solutions that everyone can share in and improve on and so on.
So its the sheer weight of numbers that become interested in whatever is the standard technology that drives that technology along. So it is very difficult for the unique technologies to survive in an environment like that. And the PERC is a very robust technology, like the aluminum back surface field, so it can be used in any type of wafer, any polarity, multi or mono, so it is robust in that sense.
In the lead up to the SNEC trade show in Shanghai later this month, pv magazine is focusing on a series of technologies currently being rolled out into commercial production. A special 20-page Technology Highlights digital publication will also turn the spotlight on some of the leading technologies and providers, from solar startups to established technology suppliers.