by John Keller
The U.S. Defense Advanced Research Projects Agency (DARPA) in Arlington, Va., has chosen a third contractor -- Ascent Solar Technologies Inc. in Littleton, Colo., for the Low-Cost Lightweight Portable Photovoltaics (PoP) program to reduce the mass and cost of portable photovoltaic devices to generate solar power for aerospace and defense applications, while maintaining high efficiency in power conversion for these new portable solar panels that generate electricity from sunlight.
DARPA awarded a $3.8 million contract to Ascent Solar this week for the PoP photovoltaics program to reduce the mass and cost of portable photovoltaic devices to generate solar power for aerospace and defense applications, while maintaining high efficiency in power conversion. Earlier this month DARPA awarded a $4.5 million PoP contract to Science Applications International Corp. (SAIC) in McLean, Va., and in March made a $1.2 million PoP award to SiOnyx Inc. in Beverly, Mass.
The PoP program is to develop technologies to reduce the mass and cost of portable photovoltaic devices, yet support high power conversion efficiency. Specifically, DARPA is asking the three contractors to develop new integrated photovoltaic technologies that have at least 20 percent power conversion efficiency under air mass 1.5 illumination at one sun in a size that lends itself to low-cost production on flexible substrates.
The contractors will build durable, portable, flexible devices at low density. To do this DARPA is considering technologies that incorporate thin-film semiconductors, microcrystalline semiconductors, or materials with similar properties. The three companies also will address light acquisition, energy capture, carrier extraction, robust and durable portability, and flexibility, including research that requires Multiple Exciton Generation (MEG) as a critical path element.
Photovoltaics experts from Ascent Solar, SiOnyx, and SAIC are beginning the PoP work by demonstrating a portable, low-cost, low-mass, flexible and durable solar cell to generate solar energy with a power conversion efficiency comparable to stationary commercial photovoltaic panels, with an eye to developing prototypes that eventually are lightweight and rugged enough for military and aerospace applications.
The program calls for the three contractors to develop efficient, inexpensive portable photovoltaic devices in four primary areas: light acquisition and energy capture; carrier extraction; robust and durable portability; and flexibility.
In light acquisition and energy capture, the companies will develop efficient photovoltaic devices active across a broad absorbance spectrum that lose minimal photons to reflection, scattering, and related processes. Company experts will consider on-board optical techniques to boost photovoltaic efficiency and reduce device size to improve how incoming photons are captured at air mass 1.5 solar illumination gathered at 90 and 45 degrees.
Company researchers also will find ways to convert photons efficiently to electrical power by keeping electron-hole recombination and resistive losses to a minimum. Company engineers also will find engineering and manufacturing techniques to build rugged, lightweight solar panels rugged enough for military applications, with resistance to puncture and rough handling.
Finally, the three PoP contractors will consider how to develop and manufacture rugged, lightweight solar panels flexible enough to be fitted to backpacks, tents, and other curved surfaces, as well as to be transported in a wide variety of vehicles.
To develop panels rugged, lightweight, and flexible enough for these kinds of applications, experts will consider technologies that incorporate thin-film semiconductors, microcrystalline semiconductors, or materials with similar properties.