The idea to use fool’s gold rather than silicon or thin film for photovoltaic solar cells is an idea developing out of Switzerland that is gaining credibility, sophistication and technical success. Fool’s gold, the shiny mineral found in some rocks is dirt cheap and comparatively easy to make molecule. The technical description is a mineral pyrite, or iron pyrite, an iron sulfide with the formula FeS2. NLV Solar AG, Zug, Switzerland a part of The NLV Group of companies has of 20 years’ research on virtual reality simulation and digital prototyping invested in the development of the innovative ‘Pyradian’ solar cell. (Please note, the links and PDFs are large files coming from Europe. They are worth the wait.)

Composites of iron and sulfur have been considered in the past for use in photovoltaic cells, mainly for their good absorption qualities. Pioneering work on the potential of pyrite as a semiconductor was conducted in Germany and has now been picked up in China. The naturally occurring iron-sulfur compound, pyrite, has several inherent problems – such as high resistance and surface currents – which are only now being overcome. On the strong side of the known material properties of modified iron-sulfur composites, it can be expected that industrial-scale production of corresponding solar cells should be feasible in the near future. Additionally pyrites both natural and manufactured are non-toxic so being harmless in production, processing and disposal.

NLV’s work has resulted in promising new properties:

  • Average photovoltaic conversion efficiency of 38%, depending on ambient conditions, and a peak performance of over 50%.
  • The possibility of fine-tuning the material’s absorption characteristics by modification of its crystal lattice structure using ion implantation; stacked in a multilayer thin-film cell, it would be possible to tune each layer to a different light target absorption frequency.
  • As a thin-film cell, the material could be applied to substrates in a transparent, semitransparent or tinted coating.
  • The projected degradation coefficient is only 5-6% over 20 years.

NLVs Pyrite Charge Properties. Click image for a larger view.

NLVs Pyrite Charge Properties. Click image for a larger view.

NLV’s proprietary Pyradian material has a very high coefficient of light absorption, reaching peaks of over 50%, with a bandwidth of α > 105 cm-1 for λ < 1 μm – significantly higher, over a broader band of frequencies than any conventional absorption material used in photovoltaics, for example silicon, cadmium telluride, copper indium diselenide or gallium arsenide. Research indicates a higher sensitivity in the frequency range of visible light, extending into the infrared and ultraviolet spectra, as well as a band gap in the range of 0.95–3.6 eV, depending on the sample. Unlike conventional absorption materials, this iron-sulfur composite also shows a workable level of conversion in diffuse light.

The iron component is critical for the longevity and the proportion to sulfur is crucial to the material meeting the specifications. Built into a crystal lattice structure pyrite is stable and in the synthesized form even more so. Compared to silicon or thin films that can drop the performance coefficients by 10 to 15% in the first year, pyrite holding 90% for over 25 years looks like a strong market contender.

The synthesized pyrite can be applied to the support structures as a thin film coating using chemical vapor deposition in a clean room type of production facility. Used strictly as a photovoltaic film application to glass, it can be nearly fully transparent when applied at low efficiencies to opaque when applied for maximum productivity.

NLVs Transparent Conductor. Click image for more.

NLVs Transparent Conductor. Click image for more.

NLV points out they have two keys, skills in optimizing the material and mastery of the engineering processes used in doing applications well under development. Of the skills NLV has worked through, the chemical ‘doping’ or introduction of controlled impurities to impart specialized characteristics, and the development of multilayered structures to enhance the total light absorption. Doped and stacked NLV tunes the composite of layers to cover the far infrared to ultraviolet. Curiously, all the layers are composed of the same pyrite material, avoiding small limits on the layers. As the unit is essentially one material, layers can be stacked up to 36 deep, maximizing the absorption.

Another technique that solves a pyrite problem is interconnecting the individual cells. Recall that pyrite has that resistance issue. NLV has pioneered a laser scribing technology that overcomes the resistance problem. Laser scribing offers extreme precision and offers excellent voltage outputs. It’s also a cheap way to draw interconnects, maintains transparency where desired, and eliminated the use of acid etching and silver or lead metal handling.

Looking good, isn’t it?

On the other hand is that this whole thing is based on digital modeling. NLV makes a considerable case that what they’ve learned and developed will go to working prototype. They have gone so far as to acquire a former wafer facility in Munich-Perlach, Germany and install the chemical vapor deposition, ion implantation and laser scribing equipment. The company’s report lists developments to come in the hardware and software work for the ion implantation and the layout and controls for the laser scribing process. The company notes that Germany has legislation in place that attracted them to the location. The other hand doesn’t seem empty.

What actually triggered my attention was the news that Koenigsegg, the Swedish supercar marque, and NLV Solar have joined forces to create the Quant, a four-seat solar car. This marriage of power and energy is a breakthrough the car market has been anticipating for years. A full-scale model is to be unveiled at the Geneva motor show. Much to many peoples’ surprise here in the U.S. is the car triggered more attention than the underlying technology.

NLV sees three main markets for the technology, permanent installations to offset or contribute to the grid, automotive applications and portable devices. NLV makes clear they grasp the market factors, such as a technologies time to market, competition, and installed cost. But as seen above they have some very attractive points. If cost is competitive, efficiencies are quite high, weather survivability good and a very long highly productive useful life all come to pass in production models I would suspect that market share won’t be a problem. A very long productive lifetime and high efficiency output go far to securing a customer’s long-term investment.

Meanwhile, if you, your company or your community have an unused clean room looking for a user you might want to get in touch with NLV.

Solar Cells - The Best Research Efficiencies.  Click image for a larger view.

Solar Cells - The Best Research Efficiencies. Click image for a larger view.

That’s three, silicon, thin film and pyrites. Let the market fight begin.


10 Comments so far

  1. Carl Andrews on March 10, 2009 1:41 PM

    At least two statements in this article show a lack of adherence to science and systems analysis:.
    1) “Unlike conventional absorption materials, this iron-sulfur composite also shows a workable level of conversion in diffuse light.” Conversion of diffuse light depends mostly on the optics of a collector, not the absorber material…other semiconductors that can convert diffuse light just fine, given a good optic to collect it.
    2) “Compared to silicon or thin films that can drop the performance coefficients by 10 to 15% in the first year, pyrite holding 90% for over 25 years looks like a strong market contender.”
    First, to contend in the market it would also have to contend with Gallium arsenide and Gallium Antinomide, both of which have PROVEN life cycles over 50 Years, with ultra-low degradation. This can be calculated due to the difference in the degradation environment between earth and space, where they have been tested for over 20 years. Secondly, the statement about pyrite’s life cycle is so highly speculative, based solely on digital simulation, that it does not warrant ANY statement about contending with competitors.

    Economically, the idea of 50%+ conversion is not competitive, because it involves multi-layer crystal lattice alignment, which can only be done with about 7 million USD of equipment per workstation, and the typical load pattern of buildings only requires about 30% electricity, whereas the other 70% load is thermal, and a much simpler hybrid solar collector that converts 30% to electricity and the rest to heat would out-perform economically and practically on a systems theory basis. If you want to know more about how you can get involved with solar hybrid systems that will take over the market, contact me. Carl

  2. Brian Westenhaus on March 10, 2009 4:39 PM

    With all due respect to Carl, everyone needs to be aware that any structure exposed to the elements will have degradation. Its the rate that matters. The issue is localized, as the components of the air is nearly uniform, its the local chemistries and pollutants that will matter especially as they react, mostly as oxidation. The mineral solar films “look” to last the longest, but time will tell.

    As for diffusion – few market ready solar cells use optics. Cost is a prime factor for going to market and adding optics isn’t providing a value in commercial products.

    Gallium products are great, that’s a certainty, but almost no one has NASA’s budget to invest with.

    Carl raises valid points, its just applicability of the points that must be put in proper perspective.

    I’ll let the self promotion stay up for a while. Just be sure you know what you’re doing if you’re using consulting services.

  3. Christopher Staffa on March 4, 2010 12:15 AM

    All indications indicate that NLV Solar is almost entirely glossy marketing without any actual products. And “the car triggered more attention than the underlying technology” because (the model of) the car actually existed, whereas the underlying technology seems to be wishful thinking.

  4. G.Ramachandram on April 19, 2010 3:56 AM

    I wished that Nlv Solar is going to lead the developments from the front.I am really confused,rather at dismay to read the observations above.I needed one such company to assist me to make my dream of a solar car a reality.Can anyone can help me\

  5. G.Ramachandram on April 19, 2010 4:01 AM

    I request the learned in the industry and Technology to help me do a 100%solar car in India,where the current temperatures are at a thretening level of 42 degree centigrade.

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  7. Leo Blesofsky on May 19, 2011 2:36 AM

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  8. Mertie Norwell on September 7, 2011 8:59 AM

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  9. Corinne Rhein on September 16, 2011 1:57 PM

    Interesting read, perhaps the best article iv’e browse today. We learn everyday cheers to you!

  10. Claud Smale on September 27, 2011 1:46 AM

    Thanks for posting. Good to see that not everyone is using RSS feeds to build their blogs 😉

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