The GreenStalk

CIGS’ Complexity Paradox

Posted in Solar by Paul Grana on May 12, 2010

Thin-film solar research is largely a two-party system.  Its two dominant ideologies are cadmium telluride (CdTe) and copper indium gallium (di)selenide (CIGS), the two different semiconductors used as the active PV layer.  And like politics, you can find people who argue the merit of each side – sometimes, beyond the point of reason.

Both technologies have loads of promise: module efficiencies upwards of 15+%, and costs of around $0.50/watt.  But the similarities end there.

Supporters of CIGS point to its versatility (can be manufactured in dozens of ways, including methods at room temperature and room pressure), and its higher theoretical efficiency (its bandgap physics is better, plus the highest CIGS cell efficiency is 20.1%, while CdTe is 16.5%).

Supporters of CdTe point to its simplicity – the active layer requires just two components (CdS and CdTe), which are deposited right next to each other… while CIGS actually requires at least six components (C, I, G, S, plus Sodium, Sulfur, and CdS) in a much more complex configuration.  Oh, and the CdTe camp has First Solar: the powerhouse with a multi-billion backlog, 1GW of production capacity, and gross margins north of 40%, even in a horrible solar market.

So if these technologies are both legit, then why the imbalance in venture capital funding:

Thin-film startups that have raised $100MM+ in the last ~4 years:
CIGS Cadmium Telluride
Heliovolt Abound Solar

(You could also set the bar lower (e.g. startups to raise $20MM+), and the list would look similar (add Stion to the CIGS side).  And I’ve heard anecdotally from VCs that the number of business plans that went unfunded had a similar bias toward CIGS.)  So how did CIGS get so much more money, while CdTe has the only ‘victory’ (FSLR) to date?

One Theory

Recall the point I made above: CIGS is way more complex (six or more components), and it is way more versatile in how it can be deposited (ink deposition, electroplating, sputtering, chemical vapor deposition, etc).  Now, put yourself in the shoes of a materials science PhD candidate at Stanford, or a researcher at NREL.  Which semiconductor would you study?  There are probably 10x more ‘interesting’ problems on the CIGS side.  And in general, an interesting problem leads to an interesting solution, which leads to getting published.

Continuing this logical chain… CIGS gets more research, therefore more CIGS patents are filed.  More companies are founded around CIGS, and more talented management teams are built around CIGS.  Ultimately, this would lead to more VC money flowing to CIGS.

The Implication

The thing I find most interesting, if this is correct (with stress on the “if”): it illustrates a direct conflict between the academic research community and the venture capital community – groups which otherwise have a very symbiotic relationship.  Academia is pulled toward complexity, because that presents more novel research topics.  However, for commercialization, simplicity is likely to be more profitable than complexity.

This may be changing.  The venture and research communities learn quickly, and all the companies above were funded circa 2005-2009.  Sequoia’s more recent investment into SunPrint is a small signal of the increased focus on simplicity & manufacturability.

Final notes:

  • Apologies to the amorphous silicon crowd for not including you in the ‘thin-film research’ category.  But my focus here is on academic research and venture funding, where I haven’t seen a-Si being actively pursued with the same vigor.
  • Anyone have any ideas for data I could find to test this hypothesis?  Besides simply counting patents, is there any good way to track the papers published, by type of semiconductor?
  • A request to those who are well-versed in fuel cells or electrochemical batteries – could this same phenomenon be playing out in those markets?  Are complex technologies getting disproportionate funding?

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