The nanotech revolution in solar power

Nanotechnology promises to deliver a breakthrough is solar cell fabrication. New nanoparticle inks are being used to make spray-on solar cells. By replacing vacuum deposition with printing, these nanoparticle inks enable continuous roll-to-roll production of solar panels. Nanotechnology looks set to transform the economics of solar energy.

Nanosolar’s first solar panels.

“The real innovation is that we’re trying to move the photovoltaics industry from the economics of the semiconductor business to the economics of the printing business.”

Erik Straser, MDV-Mohr Davidow Ventures,
investor in Nanosolar Inc. ^[1]

Traditional solar cells are fabricated using vacuum deposition. A batch of substrate wafers is placed in a vacuum chamber, the chamber is evacuated, and the semiconductor material is deposited onto the substrate. The completed solar cells are then removed from the vacuum chamber, and the next batch of substrate material is put in. The process is slow, and the vacuum processing requires expensive capital equipment.

While vacuum deposition technology has certainly been a good way to make half-inch wide computer chips, it is poorly suited to producing solar panels by the acre. That’s why solar panels have remained uneconomic as energy sources.

Breakthroughs in nanotechnology have transformed the picture. Several companies have developed nanoparticle inks that can be sprayed onto flexible substrates to form layers of semiconductor. A solar panel can simply be printed onto a roll of thin foil. These processes don’t need vacuum chambers, and in many cases they can even use conventional printing equipment.

It’s a clean break with the past. The vacuum deposition processes inherited from the semiconductor industry have been replaced with spray-on ink technologies more akin to the processes used in the printing industry. These nanotech processes can produce cheap solar panels by the acre, finally delivering on the promise of low-cost solar energy. 2008 looks like a defining year for these technologies, as some of the key companies move from development to large scale production.

Here are four of the most prominent companies in printable nanoparticle ink technology:

• Nanosolar Inc.
  The best known company in the field is Nanosolar. With its talent for self-promotion, it has served as the poster boy for the technology. Founded in 2002 ^[2] by the serial technology entrepreneur Martin Roscheisen, Nanosolar has raised over $100 m in funding ^[3], and famously counts the Google founders Sergey Brin and Larry Page among its investors. The company has developed a nanoparticle semiconductor ink ^[4] that can simply be printed onto a roll of conductive substrate material. The process is many times cheaper and faster than conventional semiconductor processing methods. Nanosolar shipped its first solar panels in December 2007 ^[5]. It claims that its products halve the system cost of solar panels ^[6].
• HelioVolt Corporation
  HelioVolt has also developed a solar cell technology based on a spray-on nanoparticle ink. Like Nanosolar’s, it is based on a semiconductor called copper indium gallium diselenide, or CIGS. The ink can be sprayed onto a variety of construction materials, such as glass and steel, to produce so-called “building integrated photovoltaic” (BIPV) ^[7] systems. HelioVolt raised $101 m in venture capital investment in 2007, and in December 2007 it announced plans to build its first factory  ^[8].
• International Solar Electric Technology (ISET)
  International Solar Electric Technology is the longest established company working on CIGS nano-ink technologies. Formed in 1985 ^[9], it had been pursuing this approach long before it became fashionable. It hasn’t sought investment, preferring to rely on government R&D contracts to develop its technology. In contrast to the high-tempo, high-profile nature of the venture capital funded companies, it has developed at a slower pace.
• Konarka Technologies, Inc.
  

  Konarka’s Power Plastic ® solar cells.

  Konarka’s founders include the Nobel prize winner Alan J. Heeger, a pioneer in semiconducting polymers. Konarka’s technology uses a fullerene ink deposited onto a polymer to form a polymer:fullerene solar cell ^[10]. Like CIGS semiconductor inks, the fullerene ink can be printed inexpensively onto flexible substrates using roll-to-roll manufacturing. The company raised $45 million in 2007 ^[11], on top of its earlier financing. It demonstrated the first inkjet printed solar cells in early 2008 ^[12].

Companies like these have made solar energy one of the hottest investment opportunities in the semiconductor industry. They promise commercially viable solar power that can match the price of grid electricity. They look set to free the solar energy industry from the subsidised niche it currently occupies. They also threaten to wipe out some of the established players – these companies have a truly disruptive technology.

References

1. World’s Largest Solar Plant Planned in Bay Area, P. Rogers, Renewable Energy World, June 22, 2006
2. History and Milestones, Nanosolar.
3. Nanoparticle Ink, Nanosolar
4. Nanosolar Secures $100,000,000 in Funding, Nanosolar Press Release, June 21, 2006.
5. Nanosolar Ships First Panels, Nanosolar blog, December 18, 2007
6. Products, Nanosolar
7. Power Buildings, HelioVolt.
8. HelioVolt Plans its First Thin Film Solar Factory in Austin, Texas, Heliovolt Press Release, December 20, 2007
9. Company History, International Solar Electric Technology (ISET)
10. High Photovoltaic Performance of Inkjet Printed Polymer:Fullerene Blends, C.N. Hoth, S.A. Choulis, P. Schilinsky and C.J. Brabec, Advanced Materials 19, 3973–3978 (2007)
11. Konarka Secures $45 Million in Private Capital Financing, Konarka Press Release, October 1, 2007.
12. Konarka Announces First-Ever Demonstration of Inkjet Printed Solar Cells, Konarka Press Release, March 4, 2008