NEWS

 

Semiconductor Today
December 31, 2007

Copper indium gallium selenide (CIGS) photovoltaic technology is making its first steps from investor promise to physical products. Furthermore, Nanosolar of San Jose, CA, USA has won a contract to supply panels for a solar power plant located on a former landfill site owned by one of the largest waste management companies in east Germany.

The project will be based on Nanosolar’s ‘Utility Panel’ in combination with systems technology and services from Beck Energy of GmbH of Kolitzheim, Germany. The initial size of the plant is planned to be 1MW (sufficient to power 400 homes).

The Utility Panel is the first product in Nanosolar’s PowerSheet product line, which is designed as a solution for solar power plants on free fields at the outskirts of towns and cities.

“After five years of product development – including aggressively pipelined science, research and development, manufacturing process development, product testing, manufacturing engineering and tool development, and factory construction – we now have shipped first product and received our first check of product revenue,” says Nanosolar’s CEO Martin Roscheisen on the company’s blog.

Nanosolar was founded in 2002 and claims that it is building the world’s largest solar cell factory (in San Jose, covering an area of 140,000ft²) and the world’s largest panel-assembly factory (in Berlin, Germany, covering 507,000ft²).

The first panel off the production line is to be kept at Nanosolar and the third is being donated to the Tech Museum in San Jose. The second panel was initially put up for sale on eBay but, when Nanosolar decided the proceeds should be donated to charity, fell foul of the auction site’s regulations (since eBay is wary of becoming liable for violation of charity laws). From starting at 99 cents, the panel had reached $13,000 when it was taken off the market with more than six days left for bidding. Nanosolar will keep the panel for the time being.

Nanosolar describes itself as being in the ‘third wave’ of solar power development (the first wave refers to the silicon-based solar cells of 30 years ago, and the second to the development of commercial thin-film technology a decade or so ago). Nanosolar believes that it has tackled shortcomings of previous solar technologies with seven innovations: the use of nanoparticle inks, semiconductor printing, conductive substrates, roll-to-roll processing, low-cost top electrode, sorted cell assembly into modules, and creating a high-current panel.

The ink contains the CIGS semiconductor material. According to Nanosolar, the four elements have to be in just the right atomic ratios to each other, locking in a uniform distribution. The homogeneous mix of nanoparticles in the ink in just the right overall amounts ensures that the atomic ratios of the four elements are correct wherever the ink is printed, even across large areas of deposition. This enables a low-cost roll-to-roll printing process in contrast to usual vacuum deposition processes where, due to the four-element nature of CIGS, one has to atomically synchronize various material sources.

The ink is printed onto a conducting metal foil substrate rather than having to deposit an additional metal thin-film bottom electrode on a non-conducting substrate such as glass or polymer. Nansolar claims that its metal substrate is 20 times more conductive than the stainless steel used by most of its competitors. It also claims a lost-cost top electrode that supports an order of magnitude higher current than previous technology. Top electrodes have to be both conductive and transparent to allow light into the semiconductor layers beneath.

The company also claims to have dealt with problems of the electrical mismatches between cells in assembled panels that lead to significant power losses. All told, Nansolar claims that its products deliver 5-10 times higher current compared with other thin-film solar panels on the market today. However, detailed specs seem to be hard to come by.