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.
(POR) The following summarizes six project outcomes for awards to GIT through the SiSoC program. Gettering and Passivation of Defects in Low-Cost c-Si Materials Here, we advance understanding of defects in low-cost silicon materials and mitigate its effect on the performance of solar cells. Process-induced gettering and passivation strategies were developed and applied to low-cost materials for multicrystalline Si solar cells effeciencies of 16-17%. This key findings obtained from this research are summarized below: Simple, approximate model developed to assess the effect of electrically active defects on VOC The mechanism of defect/impurity hydrogenation was investigated in defective String Ribbon material. Short anneal times favor lifetime improvement. An average cell efficiency of 15.7% with a best cell of 16.4% on 243.4 cm2 multicrystalline Si solar cells was achieved. Fundamental Understanding of a Boron Emitter and Back Surface Field Here, we present a process for boron diffusion compatible with low cost, low quality materials. Boric acid, cheap, safe and widely available, is used as dopant. This key findings obtained from this research are summarized below: Developed process for boron diffusion in silicon using a spray or spin-on source and maintained a bulk-lifetime of >100 μs. Demonstrated BSRV for boron BSF better than that for Al BSF. Iron contamination and gettering addressed. Boron diffused surface passivation demonstrated. Fabrication of n-type cells with thermal oxide/nitride stack passivation. Implementation of Optimized Gettering and Passivation Strategies for Multicrystalline Silicon Solar Cells with Focus on Grain Size Dependence and Advance Features Here, we optimize gettering and passivation for crystal grain size and defect density. Advanced physical and electrical features drive multicrystalline silicon solar cell efficiencies to 17-18+%. This key findings obtained from this research are summarized below: Showed the effect mc-Si wafer grain size and distribution has on final cell performance. Discussed factors contributing to cell performance based on Si grain size distribution. Investigated new and immerging monocast Si material, showing cell efficiencies can be comparable to Cz Si, and more work necessary to continue to close the gap between these two materials. Demonstrated 19% cell efficiency on cast Si materials through implementation of advance features. Understanding and Development of Dielectrics for Backside Passivation of Low Cost, High Efficiency Silicon Solar Cells Here, we explore and develop back side passivating dielectric films amenable to local back surface field formation to achieve effective surface recombination velocity Seff of < 200 cm/s so that a combination of high back surface reflectance (BSR) and effective backside surface passivation to drive silicon solar cell efficiencies to 20% and beyond. The key findings obtained from this research are summarized below: Modeled and quantified the benefit of dielectric back surface passivation. Performed modeling to establish the requirements for dielectric properties. Investigated the passivation quality of various Oxide-Nitride stacks. Investigated the passivation quality of SiCN. Demostrated 19.6% cell efficiency and showed that back surface finish, rear oxide thickness, dielectric charge and interface quality, and local BSF design, all play an important role in providing excellent back passivation without rear parasitic shunting. Development of 19% Efficient 243.4 cm2 Cast Multicrystalline Si Solar Cells through Material Quality Enhancement and Implementation of Advanced Design Features Here, we push solar cells made on cast Si materials up to and beyond 19% efficiency through the use of extensive array of process, modeling, and characterization tools available at GIT. This includes application of process protocol identified in previous projects (getting and passivation of bulk defects and use of surface passivating dielectrics to achieve low BSRV and high BSR). This project is still in its first year, but key findings already obtained from this research are summarized below: Investigated lifetime limiting defects as a function of casting methods ranging from high quality-low manufacturablility to lower quality-more manufacturable. Begun application of advance features like boron BSF, selective emitter, etc. to quantify efficiency gains possible on wafers from ingots showing a broad range of quality. Development of Advanced N-type Devices with focus on Bifacial and Back Junction Architectures to achieve > 19% Efficiency The objective of this work is to develop n-type Si solar cell technologies to better assess viability and drive to commercial production. A roadmap toward high efficiency will be developed through modeling. We will address the formation of boron emitters and the challenges that come with high temperature boron processes. We will investigate both mono- and bifacial as well as rear junction devices. This project is still in its first year, but key findings already obtained from this research are summarized below: Demonstrated effective removal of boron rich layer after boron emitter formation. Lifetime degradation of final device attributed to injection of impurities from boron rich layer.
