A solar cell is a semiconductor device that converts photons, or light, into electricity. The most widely used solar cells today are made from wafers of mono- or poly-crystalline silicon.
Poly-crystalline silicon, or multi-crystal silicon, is created by casting molten silicon in blocks. While this process is a little less expensive and faster than the process used for growing a single crystal, the resulting multi-crystal silicon is less efficient than its single-crystal counterpart.
Although less commonly used, a third type of solar cell, called a thin film solar cell, can counterbalance many of the disadvantages associated with mono- and poly-crystalline silicon manufacturing by using only a fraction of pure silicon. Thin film solar cells are made by depositing a very thin layer of silicon (or another semiconductor substance, depending upon the application) on a very thin supporting material, such as glass, plastic, or metal foil. This process is known as chemical vapor deposition.
A non-crystallized silicon known as amorphous silicon is the semiconductor material most frequently chosen for deposition, because it is a strong absorber of light. According to the U.S. Department of Energy, amorphous silicon absorbs solar radiation 40 times more efficiently than single-crystal silicon, and a thin film only about 1-micrometer (one one-millionth of a meter) thick containing amorphous silicon can absorb 90 percent of the usable light energy shining on it. Peak efficiency and significant reduction in the use of semiconductor and thin film materials translate directly into time and money savings for manufacturers.
Iowa Thin Film Technologies, Inc., of Boone, Iowa, worked closely with the Photovoltaic & Space Environments Branch so that both parties could broaden their understanding of thin film solar cells made from amorphous silicon. The commercial payoff of this alliance has now been realized, with terrestrial trickle-downs coming in the forms of solar-powered headset radios for recreational use and battery chargers and solar tents for military operations.
Iowa Thin Film Technologies also received funding for this project from several other government agencies, as well as from private resources. The private investments provided the financing necessary for the company to build a complete production facility. In addition to expanding its workspace, the company expanded its workforce, growing from just a few employees to 12 full-time and 8 part-time employees.
Because of the NASA SBIR support that led to new technology and helped create new jobs, the company today shines as a leading producer of thin film photovoltaics.
PowerFilm Solar, the solar division of PowerFilm, Inc. (the company previously known as Iowa Thin Film Technologies), manufactures and markets a differentiated line of next-generation, amorphous silicon, thin film solar panels that can easily and economically be integrated with consumer and military products. The amount of amorphous silicon used in the panels is as low as 1 percent of the amount used in traditional crystalline silicon solar panels, according to PowerFilm Solar.
“Imagine taking paper-thin plastic film and making it generate power again and again. That’s what PowerFilm is and does,” claimed Michael Coon, the company’s chief operating officer. “This is not your father’s solar technology from the ’70s. PowerFilm’s durable plastic base is superior to fragile glass or corrosive metal,” he added.
Available in a variety of standard and custom configurations to meet specific voltage, current, and environmental needs, the rollable PowerFilm products boast a durable and aesthetically pleasing design, and are quickly adaptable within their intended market, be it commercial or military. Moreover, they are not hazardous to human health, since amorphous silicon is completely free of cadmium (a naturally occuring metallic element known to produce toxic effects in humans), unlike many other solar technologies.
Other features include an internal antenna for powerful reception, a dual headband for added comfort, all-weather durability (Some users have remarked on the usefulness of the headset while walking/jogging in the rain or while boating.), and an extended bass range for setting graphic equalization to a listener’s liking.
The sophisticated solar cells also serve as precision chargers for AA batteries. In 2005, PowerFilm Solar launched the PowerFilm Foldable Solar Charger that can recharge up to four AA batteries at a time, to optimum level, without inducing damage associated with overcharging. “Unlike other solar chargers for AA batteries, this new charging circuit does not get confused from variations in current typically seen from a solar panel,” noted Frank Jeffrey, PowerFilm’s chairman.
Also in 2005, PowerFilm Solar teamed up with the U.S. Army to supply PowerFilm-equipped tents. The largest tent ordered by the Army is a canopy that can provide up to 2 kilowatts of power. “This is enough energy to power up to 66 laptop computers or 260 cell or satellite phones [when the sun is shining],” said Steve Martens, the president of PowerFilm. “A second, smaller model can produce enough power for 5 laptop computers or 24 cell or satellite phones,” he added. The power generated by each tent is stored in a bank of batteries.
The solar tents help meet the Army’s growing demand for rapid-response rates and portable, remote power, and eliminate the need for noisy generators, spare batteries, and excessive fuel storage.