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 FeS 2 . 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.

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.

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.

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

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