How Thin-film Solar Cells Work

Production of Thin-film Solar Cells
Nanosolar makes thin-film solar cells by depositing layers of semiconductors on aluminum foil in a process similar to printing a newspaper.
Nanosolar makes thin-film solar cells by depositing layers of semiconductors on aluminum foil in a process similar to printing a newspaper.
Courtesy Nanosolar

Cost has been the biggest barrier to widespread adoption of solar technology. Traditional silicon-wafer solar panels require a complex, time-consuming manufacturing process that drives up the per-watt cost of electricity. Non-silicon thin-film solar cells are much easier to manufacture and therefore remove these barriers.

The biggest recent breakthroughs recently have come with CIGS-on-foil manufacturing. Nanosolar makes its solar cells using a process that resembles offset printing. Here's how it works:

  1. Reams of aluminum foil roll through large presses, similar to those used in newspaper printing. The rolls of foil can be meters wide and miles long. This makes the product much more adaptable for different applications.
  2. A printer, operating in an open-air environment, deposits a thin layer of semiconducting ink onto the aluminum substrate. This is a huge improvement over CIGS-on-glass or CdTe cell manufacturing, which requires that the semiconductor be deposited in a vacuum chamber. Open-air printing is much faster and much less expensive.
  3. Another press deposits the CdS and ZnO layers. The zinc oxide layer is non-reflective to ensure that sunlight is able to reach the semiconductor layer.
  4. Finally, the foil is cut into sheets of solar cells. Sorted-cell assembly, similar to that used in conventional silicon solar technology, is possible in Nanosolar's manufacturing process. That means the electrical characteristics of cells can be matched to achieve the highest panel efficiency distribution and yield. CIGS-on-glass solar panels don't offer sorted-cell assembly. Because their panels consist of cells that are not well matched electrically, their yield and efficiency suffer significantly.

The presses used in semiconductor printing are easy to use and maintain. Not only that, very little raw material is wasted. This contributes to the overall efficiency of the process and drives down the cost of the electricity generated by the solar panels. Electricity from traditional solar panels costs about $3 per watt. Conventional wisdom suggests that solar will not be competitive until it can produce electricity at $1 per watt. Nanosolar claims that its super-efficient manufacturing process and revolutionary semiconducting ink can reduce the cost of making electricity from sunlight to a mere 30 cents per watt. If that holds true, solar may finally be competitive with coal.

Staff Engineer Addison Shelton works with a solar cell production coater at Nanosolar.
Courtesy Nanosolar

Thin-film solar technology is not science fiction. Nanosolar currently has a 12-month supply of orders it's trying to fulfill. Customers include corporations and municipalities all over the world. Other thin-film solar cell manufacturers are just as busy. Ohio-based First Solar is working with Juwi Solar to construct a 40-megawatt thin-film CdTe solar field in Saxony, Germany, that will be completed in 2009. And Honda is actively experimenting with building-integrated thin-film CIGS on a facility in Japan.

If thin-film solar cells achieve their full potential, however, it's easy to imagine a future where solar power is as ubiquitous as, well, sunlight. Thin-film cells could blanket the roofs or form fa├žades of buildings across cities. They could be integrated into roofing shingles for easy installation in every new house being built. And they could help power a new generation of solar cars and trucks.

For more information on solar power, electricity and related topics, see the next page.

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