SILICON NITRIDE ANTI-REFLECTION COATING
Cost-effective Efficiency Booster
General Plasma is an innovation leader in large area vacuum coating systems and sources. The patented (and patent-pending) source technologies, superb mechanical engineering and attention to detail make General Plasma products the best in their class. General Plasma is developing a family of coating systems that deliver order-of-magnitude improvements in deposition rates, uniformity, and cost of ownership.
On the occasion of management change and introduction of new technologies, InterPV had an opportunity to do an interview with Mark George, Director of Research at General Plasma.
REPORTED BY SARAH JEONG (PVED1@INFOTHE.COM)
What are the core technologies of silicon nitride anti-reflection coating?
Hydrogenated Silicon Nitride (SiN) thin films are an important technology for improving the efficiency and economics of crystalline silicon solar cells. The existing techniques of SiN anti-reflective coating are:
• Direct Plasma Enhanced Chemical Vapor Deposition (PECVD)
• Remote PECVD
General Plasma has developed an innovative new plasma technology for PECVD of hydrogenated silicon nitride. This PECVD technology overcomes problems with electrode coating, poor uniformity and slow deposition rates associated with other PECVD platforms. The uniformity of deposited silicon nitride using PECVD technology is ±3% over substrate widths exceeding 1 m which is ideal for economical production of crystalline solar cells. In addition to uniform deposition over large area, our PECVD technology enables the control of refractive index, hydrogen bond density and Si-N bond density which are important for passivating defects as well as optical matching to n-type emitters of crystalline silicon solar cells.
Through the silicon nitride anti-reflection coating, how much efficiency has been increased compared with normal coating?
Hydrogenated silicon nitride films can improve cell efficiency by 0.3% to 0.5% over TiO2 or sputtered silicon nitride films depending on cell architecture.
What do you think of the future market prospect for silicon nitride anti-reflection coating?
Currently, the market for SiN anti-reflective coating equipment is dominated by a small number of players (Roth & Rau, Centrotherm, Shimadzu). Large-scale antireflective coating market growth is taking place in turnkey production lines as the most efficient means for new manufacturers to bring new capacity online in an attempt to meet underserved demand. However, as the marketplace matures, industry opinion holds that turnkey production lines will become highly commoditized leaving the manufacturer with few options for competitive advantage. By having a single, focused product offering, General Plasma’s Maxum 1000 can offer superior performance metrics to differentiate producers in later stages of the market and, thus, are well suited for sales growth as the market matures.
Recently, General Plasma Inc. has gone through management change including vice president and sales representatives. What do you expect from the change?
With so much demand for solar, we felt it was imperative to have a strong sales and support representation in this important market. We have enthusiastically hired sales personnel to expand our entrance into different geographic regions. Our sales force is carefully selected for their commitment to excellent customer service. The new additions to our sales force significantly increase our sales and technical support capability. We will be able to meet the rapidly growing demand for our products and to better serve our customers around the world.
Please introduce the thin-film development laboratory in your company.
General Plasma works with our customers to develop state-of-the-art thin-film processing solutions for large area coating markets such as thin-film photovoltaics, architectural glass, web processing and other large area process applications. By engaging our design engineers, process engineers and material scientists, we leverage our laboratory to demonstrate solutions for our customers.
• Tools—vertical inline production deposition system (0.5 m x 1.0 m substrate), roll to roll 300 mm web coater, 3 development process tools, organo-metallic precursor delivery systems.
• Facilities—3 class 100 clean rooms, RCA wet cleaning station, fully permitted silane gas bunker.
• Characterization equipment—phase shift interferometric microscope, hall mobility analyzer, four point probe, UV-VIS-IR spectrometer, taber abrader, photo-conductivity decay for minority carrier lifetime measurement, I-V tester and Capacitance Voltage mercury probe.
In addition to these instruments, a fully equipped machine shop is available to rapidly modify and create new setups as required for process development activities.
Tell us one of the technical innovations you’ve achieved in recent years.
In 2009, we successfully produced an improved Transparent Conductive Oxide (TCO) using our patented plasma source. The new coating is cost effective and has performance benefits over competing films. This milestone demonstrated the practical application of GPI’s new plasma technology and was the culmination of 6 years of work progressing from conceptual prototypes to industrial plasma sources to the application of the new sources in actual industrial processes.
Below are highlights of GPI’s low cost TCO:
• 80% savings in materials and operating costs, compared to sputtered indium tin oxide
• Durable, environmentally stable SnO:F
• Efficient PECVD process
• >98% film transmission
• 1 x 10-3 Ω-cm at 200 ºC
• 8 x 10-4 Ω-cm at 300 ºC
What do you think is the competitive advantage of General Plasma in large area thin-film technology?
General Plasma has invented a novel source technology that enables large area PECVD for continuous processes such as web coating. The novel source, termed the Plasma Beam Source TM (PBS TM), has advantages over conventional PECVD sources, such as no electrode coating, high precursor dissociation and no powder formation. The PBS TM delivers high deposition rates; for example, SiO2 at > 1000 nmm/min and SiN at > 200 nm m/min. Films deposited by PBSTM include hard coatings on plastics (SiO2), barrier films (SiC, SiN), transparent conducting oxide (SnO2) and photocatalytic films (TiO2).
What is a long-term plan of General Plasma as an innovative leader in the solar photovoltaic industry?
Our charter is to develop process solutions that utilize General Plasma’s innovations in large-area plasma sources. With regards to the solar PV industry, we set out to validate our technology with the market place and to establish ourselves as a major provider of SiN coating equipment. Once we gain in-depth process experience, we will move to establish production and commercialization of one product. When our foothold in the solar market is secured, GPI plans to enter multiple markets where there is application for our technology under the form of joint ventures, complete plant sales or license agreements.
In your opinion, what does the silicon nitride anti-reflection coating technology contribute to the PV industry?
Crystalline silicon solar cells owe their high efficiencies in part to advanced high throughput thin-film technologies. These thin films serve both as optically matched anti-reflective layers and simultaneously render the surfaces of the underlying active semiconductor electrically passive. Hydrogenated silicon nitride is of keen interest because it is a key thin film for commercial crystalline silicon solar photovoltaic devices. The PV industry will benefit tremendously from a SiN coating technology that can reduce the cost and increase the efficiency of crystalline solar cells.
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