Technicians at Applied Materials test a laser scribe machine, part of the company’s equipment line for making the world’s largest solar panels. The lasers etch the outlines of solar cells into a transparent conductive oxide that coats a glass panel.
In 2006, semiconductor-equipment giant Applied Materials got into the solar-power market in a big way. At the company’s headquarters in Santa Clara, CA, you can see just how big: a ceiling-mounted crane lifts a piece of glass the size of a garage door onto a table for testing. The glass sheet, covered with a thin orange film of amorphous silicon, is destined to become one of the world’s largest solar panels.
Applied Materials developed the equipment to produce these extremely large photovoltaic panels in order to lower the price of solar power–crucial if solar is to compete on price with fossil-fuel electricity. The value of a solar installation comes down to the cost of each watt of power it can produce over the lifetime of a panel, and Applied Materials’ panels bring down costs in two ways. The equipment for manufacturing thin-film solar cells operates more efficiently when the panels are bigger. And larger modules need less hardware and labor to wire them together and support them.
Applied Materials, which was already the largest equipment supplier to the semiconductor and liquid-crystal-display industries, brought its expertise to solar power in 2006. The company’s photovoltaics and its display backplanes are both based on glass panels coated with amorphous silicon. Its production facilities were already set up to make those panels in 10 sizes, so achieving the best cost per watt was simply a matter of picking the right surface area, says Jim Cushing, senior director of the photovoltaic-equipment line. The result was “by far the fastest ramp to production in the PV industry,” he says–from lab to market in just under two years.
Applied Materials now sells a complete set of equipment for transforming large glass panels into thin-film solar cells, transporting it to manufacturers in several shipping containers. The company claims that each factory using its equipment can produce enough solar cells every year to generate 80 megawatts of power, enough to provide energy for 35,000 U.S. homes during peak hours of electricity use.
The process of building the solar panels themselves starts with glass sheets 2.2 by 2.6 meters in area and only 3.2 millimeters thick. These come to a factory precoated with a micrometer-thick film of a transparent conductive metal oxide that will serve as the top electrical contact in the finished panel. A robotic arm shaped like the business end of a forklift loads the delicate glass sheet onto the metal rollers of a conveyor belt, which moves it through a cleaner and then through a seamer that reinforces its edges to prevent chipping during manufacturing. The panel then travels through a machine called a laser scribe, which carves lines through the conductive coating to define the boundaries of each of 216 cells on the panel.
The panel is now ready to be coated with two silicon films that will absorb sunlight and convert its energy into electrical current. First is a layer of amorphous silicon, which strongly absorbs light from the blue end of the spectrum. A second robotic arm slides the panel into the airlock of an apparatus called a plasma-enhanced chemical-vapor deposition chamber. Inside, the air is pumped out; silane, a gas composed of silicon and hydrogen, is pumped in and ionized. In the resulting reaction, the gas decomposes, depositing the silicon uniformly on the glass.