This Small Business Innovation Research (SBIR) Phase II project aims to develop a Plasma-Enhanced Chemical Vapor Deposition (PECVD) system for the deposition of silicon layers for a solar cell to absorb sunlight and convert to electricity. Current PECVD processes face challenges that limit the quality and speed at which the silicon thin film can be deposited. This translates into higher capital cost and less efficient photovoltaic modules, thus higher cost. In this project, a novel microwave surface-wave plasma source for the PECVD processing step will be developed. This source has the potential to increase deposition rates by 10 times over the current state of the art, while maintaining excellent film quality needed for high energy conversion efficiency and long lifetime. The expected outcome of this project is to offer a technology with high processing speed that is suitable to manufacture advanced tandem and triple-junction solar cells with high energy conversion efficiency.
The broader/commercial impacts of this project will be the potential to enable the manufacturing of high-efficiency thin-film silicon solar cells at costs meeting or exceeding the 2020 grid-parity goal of $1/Watt installed cost. Thin-film silicon uses earth-abundant, sustainable materials with inexhaustible supply of raw materials and no toxicity concerns. The solution provided by Starfire addresses a critical manufacturing challenge that has the potential to break the thin-film silicon bottleneck and enable its wide adoption. This technology can also be used in areas such as semiconductors and advanced lighting.
This Small Business Innovation Research Phase II project investigated a new type of plasma source that could be used for manufacturing of photovoltaic devices (solar panels). Plasma is considered the fourth state of matter, beyond solids, liquids and gases. Plasma chemistry is very useful for making thin-films (fractions of the width of a human hair) since plasmas have properties that can be electrically-controlled through fields, pressure, temperature and material choices. Very expensive machines are used to generate plasmas for use in the production of solar panels. Improving the capability of a plasma source can play big dividends in terms of lower cost, higher quality and faster production. The standard plasma generator is the capacitively-coupled radio-frequency discharge. It is good at manufacturing for small sizes but has difficulty scaling to large sizes for making solar panels effectively. There are limits to the quality of product and rate of production with large size. Both of these limitations drive up the unit cost of the end product. The surface-wave plasma source addresses these deficiencies with a radical new approach. The Phase II program successfully met 5 of 6 planned milestones, demonstrating thin-film deposition of amorphous and nano-crystalline silicon at speeds 3x higher than the current state of the art. Scalability to large area with low-cost infrastructure was shown during Phase II. Methods to use this approach for the production of very high efficiency (>25%) silicon heterojunction cells was shown with a pathway for high-volume manufacturing. These encouraging findings support continues Phase III development since it may lead to advances in domestic semiconductor and photovoltaic manufacturing (jobs), address important national energy policy goals, and influence broader environmental impacts. This work has also fostered educational and mentorship opportunity for students in a research laboratory setting.