This proposal formally establishs a multi-university Silicon Solar Consortium (SiSoC) as part of NSF?s Industry/University Cooperative Research Center (I/UCRC) program. The Georgia Institute of Technology and North Carolina State University (the lead institution) will maintain research sites to collaborate on research, fabrication, and characterization of advanced photovoltaic (PV) materials and devices.
The proposed center's goal is to help reestablish a global leadership role for the U.S. Silicon PV industry by having government together with the solar-electric power industry jointly stimulate high quality university level research and education, while developing an expanded and skilled workforce. The Center will collaborate with other university and government agencies bringing together the leading academic institutions currently involved in PV research and development. Research emphasizes materials characterization leading to a fundamental understanding of impact of defects/impurities/mechanical behavior of solar cell materials to accommodate various needs of both single- and multi-crystalline Si wafers, thin films and nanoscale PV science and technology. Results will create strategies for processing advanced silicon PV structures and devices. Research will also focus on reducing the cost of PV generated electricity and designing and fabricating high efficiency solar cells.
SiSoC will help develop a skilled workforce in a much needed area. This will be enabled by having NSF and other government agencies, together with the solar-electric power industry jointly stimulating high quality university level research and education. Research activity will also be strengthened through student internships at industry member locations. This center will also be used to compliment efforts for outreach and improve opportunities for underrepresented minorities/women to participate in PV materials research through such programs as the Research Experiences for Undergraduates.
The key outcomes attained under SiSoC funding showed that the center has demonstrated multiple successes. According to data independently collected by the NSF evaluator, the center has impacted the R&D focus and financial bottom line of industry members. In 2010, ten industry members reported starting 18 new research projects valued at $1 million as a result of SiSoC research activity. In 2011, the value of SiSoC-stimulated research at member firms was valued at $2.5 million. Also, in the final year of phase I (2012), member companies reported $5.5 million in cost avoidances and savings through SiSoC research interactions as well as $1 million in new project initiation within member companies. SiSoC member companies have indicated a high level of interest in the currently funded project portfolio, with 71% of respondents showing interest in 60-80% of projects and 15% of respondents showing 80-100% of projects. This is significantly higher than average for NSF IUCRCs. These cost avoidance, savings and newly stimulated projects represent impacts derived from the combined activities at both NC State and Georgia Tech. The recent NSF report "Industry-Nominated Technology Breakthroughs of NSF Industry/University Cooperative Research Centers 2012", which involves industry nominated breakthroughs, highlights the extensive research being performed through SiSoC-funded research programs on an innovative new silicon material known as cast-monocrystalline silicon, which holds the potential to offer the low cost of traditional cast-multicrystalline silicon while capturing the high efficiency offered by Czochralski silicon. Furthermore, SiSoC research projects have resulted in more than 30 publications in high impact peer-reviewed journals and technical conference proceedings. In the recent 2012 I/UCRC Technology Breakthroughs bulletin, SiSoC research was highlighted. Below is an excerpt from this bulletin: Crystalline silicon continues to dominate the photovoltaics (PV) industry in the renewable energy market. Within silicon based solar, cast multicrystalline (mc-Si) and Czochralski (Cz) grown material account for the majority (~80%) of the PV devices. A key cost of production metric for the PV industry is the total cost of production in terms of the power produced ($/Watt). If module efficiency is fixed at 16% and the wafer cost considered, mc-Si material is significantly cheaper to produce (~0.35¢/Watt) when compared to Cz-Si (~0.50¢/Watt). Realistically mc-Si material results in a lower power output per module than Cz-Si. Even so mc-Si material currently holds a small $/Watt advantage over Cz-Si products. Traditionally much of the performance disadvantage incurred in mc-Si materials is a derivative of the growth methodology. Due to the nature of the solidification of the Si melt, the crystal segregates into smaller randomly oriented crystals and suffers from many planar dislocations. These regions serve as sinks for impurities, along with crystallographic stress defects which reduce photo-diode quality through provision of minority carrier recombination centers. This limitation of traditional as-grown mc-Si can only be overcome through advanced gettering techniques and supplemental processing which are not conducive to commercial application. Recent research at multiple companies has explored new growth techniques that seed the mc-Si casting crucible with a <100> oriented Si crystal. With careful growth rate and temperature control they are able to grow a nearly single crystalline material over a large vertical and horizontal area of a casting which maintains the seed orientation. This material is called quasi-mono, cast-mono, or mono-cast (mcast-Si). Due to the crystal orientation of mcast-Si, anisotropic texturing methods normally used for Cz-Si can be applied to the wafers during cell processing. The net result is a > 1% absolute boost in efficiency over isotropically textured mc-Si wafers (non-encapsulated). This type of material when commercially processed has obtained > 18% efficiency which is on par with Cz-Si material. The Georgia Institute of Technology (GIT) along with commercial partners has also produced > 18% conventional cells through study of growth methodology and commercial process optimization. If processes can be optimized to increase the area of monocrystalline material and the material quality maintained along with the cost reduction through other process parameters (solidification time, etc.) then the advantages of the mcast-Si material would be multi-facetted. One advantage would be the packing factor for wafers in a module. Mcast-Si wafers are 6 x 6 inches (~244 cm2) square like mc-Si wafers. Cz-Si wafers are 6 x 6 inches (~239 cm2) pseudo square in most cases with rounded corners due to growth constraints. A module can hold the same amount of mcast-Si cells as Cz-Si cells. Hence the mcast-Si material provides additional power due to maximizing the active area of the PV module. A second advantage is that the material retains the flexibility of Cz-Si for advanced cell structures needed to make the PV industry more competitive. Under application of one of GIT’s more advanced structures, mcast-Si material has achieved > 19% conversion efficiency on a full 244 cm2 substrate. This is a significant efficiency for full scale cells based on materials grown using a casting methodology.
