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Paula Mints on the Failure of Thin Films

November 13, 2010

Paula Mints is a respected member of the elite of the PV community. Her article in Solar Industry (November 2010) is not wrong, it just is not deep enough. Yes, to a great degree, thin films failed to revolutionize PV. But there are too many interesting things to discern from her data to stop there.

Perhaps Mints’ most convincing tabular evidence of the failure of thin films to revolutionize PV is her Figure 1, thin film share of total shipments. She shows that thin films’ share peaked in 1988 at 32% and plunged from there to 5% in 2004. Then it only picked up slightly to 17% by 2009. She didn’t have numbers from 2010, but given the growth of Chinese silicon, thin film share may even fall in 2010. Is this the characteristic of a revolution?

Having been part of the development of thin films, I’ll give Paula her due and say we once thought it would be a revolution. But the surprise wasn’t just about thin films – it was how good crystalline silicon could be. That’s a message I would agree with. This has to be said – crystalline silicon was better than we (the thin film community) realized; and it still seems to have plenty of potential for continued progress. There hasn’t been and there will not be any overall revolution of PV by thin films.

However, that is not “ ’nough said.”  That falls far short of ‘nough said. Because Paula’s own data shows one thing in favor of thin films and in favor of CdTe specifically – it has grown explosively, an d even more rapidly than any other technology, including crystalline silicon. And it has made a difference, along with Chinese silicon, in adding zest to PV competition, with the very desirable effect of reducing typical prices and keeping the pressure on for continuing to do so.  This is shown in Mints’ Figure 2, adapted here to show comparative CAGRs graphically:

The growth of CdTe is more than triple the growth of PV modules in general.

The lesson is thin films are not monolithic. Pick out the growth rate of amorphous and thin film silicon (purple Xs). Despite the opening made by expensive silicon, thin film silicon grew only marginally since 2004 – 38%. By comparison, CdTe (blue *) grew at 181% since 2004, three and a half times higher than the growth rate of all module shipments. This is what success looks like. To ignore the success of CdTe is to fall short in terms of understanding a crucial factor in the future of PV and to diminish unnecessarily the success of thin films to-date.

Thin films are not created equal. A bit simplistically, it’s like the old story of Goldilocks and the Three Bears. For amorphous and thin film silicon, the porridge is not hot enough. The efficiency is too low. For CIS alloys, the porridge is too hot – although CIS cells can be very efficient (20% cells!), CIS is hard to manufacture. For CdTe, the porridge is just right – efficient enough and easy to manufacture. There may be a dozen documented ways to make 10% CdTe cells.

The concept of thin films makes sense – less material, less handling through large area substrates – but it has to be executed. So far, CdTe is the only technology that has executed. But when the concept of thin films is executed, it can stand up to any competition in PV, including Chinese silicon.  Can anything else in PV say the same?

Beyond the status quo, only CIS looks like it might, someday, be a serious competitor of CdTe. And this would be good, because we need more competitors to keep the progress in PV robust and the competition lively.

There is something else to be learned about the failed thin film revolution, and this is very important, especially here in DC. A good new idea may take 30 years to pan out, and by the time it does, the status quo will have changed radically. There will very likely be no revolution, and there may not even be progress.

The technologies now in place have tremendous up-side. They will get much better and deserve the Federal support needed to keep them moving (and keep the US leading technologically). Tens of new PV ideas have been examined and dropped in comparison to them, but newcomers to PV (and I include almost everyone who comes to DC with every new Administration) make the mistake that they (1) can have a revolution in PV and (2) that we need one. We can’t, and we don’t.

For usually, when newcomers have new ideas, they are old ones – old and discarded ones that are very boring to the PV community. Plastic solar cells? Dye cells? Cells made on flexible foils? Give me a break. They exist and can be barely sold. These technologies are not terawatt-worthy. Yet often, it is just these kind of cell technologies that people new to PV fund and research when they talk of the next revolution. Someday we will have a mature PV program, when we have the patience to learn about the one we have.

So, Paula, pardon me for using your excellent story as a springboard. Your data tells a deep and important story, even beyond the necessary recognition that thin films did not revolutionize PV.

Ken Zweibel

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7 Comments leave one →
  1. Todd Flach permalink
    November 16, 2010 2:58 am

    Thanks for the straight talk, Ken. I wonder what your impression is of the new amorphous silicon products and manufacturing suppliers. Oerlikon claims a product that is very competitive with First Solar CdTe, and they do not need any rare earth metal, which could be a cost factor for CdTe in the near future. Why are you bearish on a-Si thin film?

    • gwsolar permalink*
      November 16, 2010 9:06 am

      For thirty years, I have been hearing claims by amorphous silicon companies. Meanwhile, they haven’t solved either the low efficiency or high capital cost problems. How long do they get before people simply discount their new claims UNTIL PROVEN?

      I guess there’s always a chance Oerlikon, Sharp, or someone else will succeed. It isn’t too harsh to say, let them prove it first.

  2. Todd Flach permalink
    November 17, 2010 2:52 pm

    Ken, may I remind you that for 30 years the fossil fuel industry has been poo-pooing the PV industry for its underperformance, just like you are now poo-pooing the amorphous Si thin film industry for its 30-year history of underperformance. Now, if you would be willing to tell us what is wrong with the NREL verification of Oerlikons latest a-Si product then here is your chance.

    • gwsolar permalink*
      November 19, 2010 10:35 am

      Many PV technologies have proven their value over the last 30 years. Yet there is a level of extra claims that simply adds confusion, when they are not followed with actions. Asking a-Si and thin film silicon to come up to the same standards as the rest is not asking too much.

    • Joe Beach permalink
      November 19, 2010 6:32 pm

      The big questions for the Oerlikon data are: 1) what is its degradation rate, 2) what will the real production cost be, and 3) what will the real capital cost be. The last two, in particular, will only be known when a public company produces panels with that technology at hundreds of MW of capacity. The production cost data and capital cost data are just predictions right now. Applied Materials made similar grand claims, which has given people cause for skepticism now.

      Oerlikon will also face the same challenges that CdTe faces, which are continuing improvements in efficiency and durability while maintaining a low production cost. At this point, 10% efficient panels are barely marketable. In a few years, CdTe (and any other thin film with the same cost structure) will have to be making 12% or better panels (typical performance, not hero panels) to have a product. This is part of the issue Ken mentioned, the status quo keeps changing as products are developed.

  3. December 24, 2010 1:53 am

    Excellent article Ken. And a significant acknowledgement from someone that was anticipating a different revolution.

    While I am also a strong supporter of Paula, I believe that both your view and her views do not put enough emphasis on two key points:

    1. Consolidation on a standard

    Sooner or later the industry had to pick a winner. It has, and is now consolidating on a crystalline standard. FirstSolar has managed to get on the other side of that abyss. While crystalline may be king, there are plenty of crystalline companies that may not be around in a few years.

    The consolidation/standardization helped seal the fate for Sunfab (

    As consolidation/standardization continues, costs should drop considerably. Whether pursuing thin film or crystalline, a new entrant or approach in cell manufacturing is unlikely to succeed. New manufacturing approaches and technologies will need to complement the big players and fit into their existing strategies.

    2. The brutal and compounded impact of efficiency delta competitiveness as costs drop (

    Paula’s observation that “many new entrants and investors mistook a market situation of constrained supplies, too-high incentives, and high demand for a permanent situation” is very well taken.

    Anticipating that competition will remain still, and not react to severe pressure is a classic challenge.

    Back when there was a poly shortage, many people outside crystalline forgot about what was happening to fundamental manufacturing costs. The shortage put intense pressures on crystalline product performance and cost management. At the same time, the incentives allowed factories to get larger. The combined pressure helped improve product and reduce cost. As you note, crystalline was better than the thin film community anticipated.

    FirstSolar’s growth (as illustrated in Mints’ Figure 2) has helped it to keep improving at a rate equal to or faster than crystalline.

    As Crystalline costs come down, FirstSolar will have to keep improving at a faster rate than crystalline. That is not a threat nor a condemnation. It is simply observing a trend that has already been established. It will be healthy for the overall industry – though not for new entrants – if they can keep moving quickly.

    Regards, David


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