EPV has traditionally maintained cutting edge research in the areas of thin film materials, devices, and deposition technologies. These programs are aimed at advancing thin-film PV technology through the development of novel methods and structures. Some of the hardest problems in thin-film PV are being addressed. Broadly speaking, EPV is active in two distinct thin-film PV technologies, namely, thin Si and CIGS. In both areas, EPV is pursuing advanced technologies to enable the production of next generation thin-film modules.
Thin Film & Plasma Enhanced Nano-Crystalline
EPV’s current commercial module products are based on tandem-junction amorphous silicon (a-Si). A proprietary large-batch PECVD process allows these 8.5 ft2 modules to be manufactured with one of the world’s lowest cost per watt figures. EPV is currently engaged in scaling up its technology to larger glass sizes. In addition, EPV has identified several routes by which the performance of these modules can be improved, including modification or replacement of the front TCO (currently tin oxide) and optical engineering in general. After years of preparatory invention and research, EPV has demonstrated most of the key elements and is now poised to exploit these new techniques. The most radical new element is the introduction of nano-crystalline Si (nc-Si) as a long-wavelength absorber. EPV has demonstrated stabilized efficiencies approaching 9% in hybrid a-Si/nc-Si devices. The nc-Si is produced close to the mixed-phase / microcrystalline transition edge. EPV is now working on the development of large area technology to produce modules that utilize such hybrid devices. Depending on the exact configuration, a power gain in the range of 30% – 50% can be expected.
CIGS
EPV has also acquired deep expertise in another semiconductor technology that is well suited to energy conversion, namely, copper indium gallium diselenide, or CIGS. CIGS modules offer almost twice the efficiency of a-Si modules while being only about 25% more expensive on a unit area basis, thereby reducing the cost per watt by over 30 percent. EPV has developed specialized vacuum equipment designed for heating, moving, and coating large pieces of glass with CIGS. It has also recently introduced the “simplified hybrid process” for CIGS formation. This process reduces CIGS formation time and possesses additional merits regarding module fabrication and process control. This important development is expected to make manufacturing of CIGS modules easier than by competing methods. EPV has demonstrated 14.0% efficient CIGS solar cells and 0.43m² CIGS modules. EPV is continuing to develop key technologies that it believes are a necessary prerequisite to cost-effective CIGS manufacturing.
Supporting research activities
EPV has developed linear hollow cathode sputtering sources that enable the deposition of a wide range of compound films (oxides, nitrides, carbides, selenides) in a cost efficient way. The so-called “Reactive Environment Hollow Cathode Sputtering” (RE-HCS) method is very suitable for in-line, large-area deposition. Using this technique, EPV has produced conductors, insulators, optical layers, barrier layers, semiconductors, and transparent conductors, including Al, Cu, Mo, Ni, Al2O3, TiO2:Nb, AlN, InN, TiN, InxAl1-xN, ZnO, ZnO:N, ZnO:Al, ZnO:B, In2O3:Mo, In2O3:Zr, In2O3:Ta, In2O3:Ti, ZnO:In2O3, CuAlO2, CuBO2 and others. The method can be applied in a low-damage mode, an advantage in growing electronically-active materials. EPV was the first in the world to apply RE-HCS to the preparation of transparent conductors such as ZnO:B, In2O3:Mo (IMO), and In2O3:Ti (ITiO). Excellent mobilities of over 80 cm²/Vs have been achieved for IMO and ITiO, and EPV can be said to be a world leader in developing both these and other transparent conductors. The utility of RE-HCS has been confirmed by incorporating several materials produced by this method into competitive solar cells. An industrial version of the source has also been developed. Research institutions or manufacturers of displays or flexible electronics interested in acquiring a license to this technology should contact Dr. Alan E. Delahoy, Vice President, Research & Development. EPV has also developed radical sources based on hollow cathode discharges.
Government contracts
EPV is grateful to the following agencies for past research support: the U.S. Department of Energy through the Thin Film Photovoltaic Partnership Program and the PV Manufacturing R&D Program with the National Renewable Energy Laboratory (NREL) and also through the SBIR program; the U.S. Department of Commerce through the Advanced Technology Program with the National Institute for Standards and Technology (NIST); the National Science Foundation; the New Jersey Board of Public Utilities through the Renewable Energy Economic Development Program with the Office of Clean Energy; and the New Jersey Commission on Science and Technology.