| NSF Org: |
CMMI Division of Civil, Mechanical, and Manufacturing Innovation |
| Recipient: |
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| Initial Amendment Date: | July 31, 2016 |
| Latest Amendment Date: | July 31, 2016 |
| Award Number: | 1635334 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Khershed Cooper
CMMI Division of Civil, Mechanical, and Manufacturing Innovation ENG Directorate for Engineering |
| Start Date: | September 1, 2016 |
| End Date: | August 31, 2021 (Estimated) |
| Total Intended Award Amount: | $950,001.00 |
| Total Awarded Amount to Date: | $950,001.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
1 UNIVERSITY OF NEW MEXICO ALBUQUERQUE NM US 87131-0001 (505)277-4186 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1313 Goddard SE Albuquerque NM US 87106-4343 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | SNM - Scalable NanoManufacturi |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.041 |
ABSTRACT
Solar photovoltaics market is growing rapidly on a global scale. Notwithstanding the rapid growth, the cost of installed photovoltaic solar energy system must be further reduced for a wide distribution of solar power usage in the marketplace. The difficulty has been to reduce, by a significant degree, both the material cost and the "soft cost", such as transportation and installation of solar photovoltaic modules. Addressing this market challenge, this Scalable NanoManufacturing (SNM) award will provide manufacturing solutions to reduce the material cost by first making use of thin, flexible crystalline silicon substrates, as crystalline silicon accounts for as much as 30-40 percent of a typical solar module cost. The use of thin substrates would also reduce the soft cost by enabling cells to be supported on a lightweight flexible platform. Lightweight translates to reduced transportation and installation costs. While the cost benefits are clear, maintaining the same photovoltaic efficiency from thin silicon solar cells requires significantly improved light trapping and absorption within the thin layer. The technical solution to be explored is to use periodic, nanoscale surface features with reduced symmetry to effectively couple the sunlight into the underlying silicon substrate. A manufacturable, cost-effective, high-throughput process will be developed to fabricate such nanostructures on thin silicon films. This new process will provide uniformity over a wafer-scale, bridging six orders of magnitude in length scale. The project will also help the public appreciate alternative energy sources by developing educational tools using web-based immersive interactive visualization.
Fabricating nanoscale features uniformly over a wafer scale poses significant engineering challenges. Various lithographic techniques exist today to define submicron features. However, the success of any one technique will depend on its large-scale performance and manufacturing cost. For instance, the conventional deep-UV optical steppers are highly suitable for sub-micron light-trapping features in solar cells but are overly expensive for wafer-scale applications. The research team will develop processes to scale up phase-mask-based interference lithography, where a coherent beam is projected on a pre-patterned grating mask, and the diffracted plane waves from the mask interfere with each other to make periodic patterns. The scale-up lithography processes will also involve wet etching steps to fabricate efficient light-trapping structures on thin silicon solar cells. A multiscale, multiphase transport and reaction model of the wet etch process will be developed to solve the scale-up engineering challenge. The photovoltaic characteristics of the large-area solar cells fabricated by the developed processes will be investigated on a device level.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Silicon photovoltaics accounts for a major part of solar industry. For a wide distribution of solar power usage, the cost of the photovoltaic systems should be reduced. Among numerous approaches toward this goal, one economically viable solution is to decrease the thickness of silicon photovoltaic cells while increasing their light absorption in a manufacturable way. As thin cells require highly efficient light-trapping surface nanostructures, development of manufacturable surface patterning techniques is essential for this approach. Engineering challenges for such development stems from the fact that the solar cell surface linear dimension is 5 to 6 orders of magnitude larger than that of the submicron surface features.
With support from this grant, we have developed scalable nanomanufacturing techniques for uniform fabrication of such small features over silicon wafers. We have scaled up interference lithography to fabricate the features over 4-inch silicon wafers. To ensure pattern uniformity, we wobbled a laser beam impinging on the photomask. To transfer the pattern in photoresist onto silicon wafers, etching in alkaline solution was performed. As our modeling showed, chemical reaction was much slower than diffusion in the etch process, rendering a uniform pattern.
Solar cell fabrication was performed in collaboration with the National Renewable Energy Laboratory. To enhance light trapping efficiency, we introduced symmetry breaking in submicron features by exploiting a mismatch in the lattice vectors between the silicon crystal and the surface pattern. This strategy has an advantage that no manufacturing steps are added to break symmetry. For our photovoltaic cell where a silicon layer thickness was 14 microns, the symmetry breaking enhanced the photovoltaic efficiency by 1.1 % in absolute value. At the small thickness, the cells are highly flexible and can be shaped in many different nonflat forms. When they were in a wavy film form in our testing, an increased surface area facilitated efficient heat removal especially at low wind speeds. This strategy of heat dissipation gives an enhancement in photovoltaic efficiency and would lengthen the cell lifetime.
The grant supported three PhD students and two of them have graduated with the degree. A student benefitted from an internship training in the National Renewable Energy Laboratory and is now employed in semiconductor industry. In addition, a postdoc, a research professor, and master students were supported from the grant.
Last Modified: 12/21/2021
Modified by: Sang Eon Han
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