Much had been heard about the Thin-film CIGS-based solar cells and the related research going on. University of Delaware, U.S.A has done a break through in the manufacturing process where the solar cell sheets are created by depositing copper-indium-gallium-diselinide (CIGS) on a 10-inch polymer web.
According to the University of Delaware's Institute of Energy Conversion (IEC), they have developed new technology for the manufacture of flexible solar cells, which could reduce the costs associated with the use of photovoltaic energy while at the same time expanding possible applications.
The system, in which there has been commercial interest, enables the more efficient manufacture of the flexible solar cells in long sheets using roll-to-roll reactors, much like newsprint speeding through a press.
As such, the system allows "extremely high production throughputs, thus reducing manufacturing costs," according to Erten Eser, associate scientist at IEC.
It also provides for lightweight and flexible solar cell panels that could find interest in the space, military and recreational markets. For standard applications, the solar cells can also be encapsulated into a more traditional rigid structure. By being flexible, the solar cells can conform to different surfaces. "This is particularly important for roofing applications for building integration, and for airships and balloons."
The solar cell sheets are created by depositing copper-indium-gallium-diselinide, which the IEC scientists call CIGS, on a 10-inch wide polymer web, which is then processed into the flexible solar cells. CIGS solar cells are currently the only thin-film technology that has achieved efficiencies comparable to silicon solar cells, presently the standard of the industry.
However, IEC has evaluated the quality of CIGS on the molybdenum-coated web by characterizing the uniformity of the film. Researchers found that average solar cell conversion efficiencies of 10 percent were achieved.
Thin-film CIGS-based solar cells have a multi-layer structure stacked on a substrate, in this case a high-temperature polyimide substrate that is coated with molybdenum, CIGS, cadmium sulfide, zinc oxide and indium tin oxide, according to the scientists,
"Through this all the component films of this structure can easily be processed on flexible substrates .In fact, CIGS is the most difficult layer because of high substrate temperature and thermal deposition from four different elemental sources, since this process results in the best performing solar cells."
This achievement is important because "it demonstrates the feasibility of the most challenging part of the overall process."
Other thin-film solar cells also can be made into flexible form, citing the amorphous silicon family of cells. "They are in the marketplace but have limited applications due to their low efficiencies," According to Eser.
Cadmium-telluride-based solar cells have "too many high temperature process steps to be easily made onto flexible substrates. They also require that light enter the device through the substrates, which requires the substrates to be transparent. "At the present time, high-temperature, transparent and flexible substrates are not available" for cadmium-telluride-based solar cells.
IEC researchers started developing flexible CIGS in 1995 as part of a consortium through a multi-year program funded by the Defense Advanced Research Projects Agency, which is the primary research and development arm of the Department of Defense, said Eser.
"Presently we are at a stage where we can make flexible CIGS of 10-inches in width and 50 feet in length, and which demonstrates efficiencies around 10 percent," according to Eser.