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NanoPower Research Labs

Polycrystalline III-V Solar Cells

State-of-the-art III-V high efficiency photovoltaic devices (~ 30%) have exclusively been fabricated on single crystal substrates, such as GaAs and germanium (Ge). Ge is the substrate material of choice for commercial multi-junction (MJ) III-V devices because it offers the opportunity to form a bottom photovoltaic junction as well as being more robust than GaAs. This allows the use of a thinner substrate, resulting in a lower mass and thus a higher areal and mass specific power solar cell. Unfortunately, crystalline Ge poses significant hurdles for achieving array specific powers approaching 1000 W/kg. We have been attempting to incorporate the strengths of high efficiency III-V MJ cell technology with substrates that offer significant benefits compared to the Ge typically used today.

The ability to accomplish this integration is based upon two separate laboratory demonstrations. First, >20% AM1.5 efficiency polycrystalline GaAs cells were demonstrated several years ago. The second development involves the recently demonstrated ability to re-crystallize thin amorphous Ge films deposited on ceramic plates and metal foils. Thus, by combining these demonstrated technologies and extending them to include MJ III-V devices, a pathway to high efficiency (>20%) flexible thin film solar arrays is readily apparent. A 20% efficient device could exceed 1000 W/kg on a 25 micron stainless steel foil or another mass equivalent metal substrate.

Recent Publications:
Sheila G. Bailey, David M. Wilt, Jeremiah S. McNatt, Les Fritzenmeier, Seth M. Hubbard, Christopher G. Bailey, Ryne P. Raffaelle, “Thin Film Poly III-V Space Solar Cells”, Proc. of 33rd IEEE Photovoltaic Specialists Conf. 1, pp. pending (2008).