Solar Photovoltaic
Early Stage R&D
Hot Wire Chemical Vapor Deposition with Carbide Filaments
National Renewable Energy Laboratory
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The solar market has changed dramatically over the last three years as an influx of low cost silicon (Si) and entered the market. The once high cost for solar panels, along with high margins for solar manufacturers, has been removed. The current market is characterized by consolidation, increasing competition, and steady bankruptcies. In order to gain a competitive edge, manufacturers are now looking to decrease the amount of materials used in solar photovoltaic (PV) cells. Traditionally this was done through only a few thin-film manufacturing materials and techniques, but the drop in Si has forced new methods for deposition and advanced manufacturing to be adopted.
The National Renewable Energy Laboratory (NREL) has been at the forefront of technological innovation within the PV industry. Many of the current industry cells in production have come through NREL, either through full development or improvement, creating intellectual property (IP), and verification. One deposition technology utilized at NREL deals with hot wire chemical vapor deposition (HWCVD), and holds the potential to decrease costs within the manufacturing of Si substrates. NREL scientists have discovered a unique way to quickly grow epitaxial Si using HWCVD while maintaining control of the surface morphology during the growth from smooth to pyramid shape, making it ideal for light trapping. This work pioneered the epitaxial Si growth through HWCVD and led to subsequent work and industry collaboration at NREL.
DescriptionHWCVD, also known as catalytic CVD (Cat-CVD), has emerged as a new technology that deposits materials at low temperatures without the use of plasma to decompose source gases. Since this technique is thermal in nature, it relies on a heated metal filament to decompose the gas species, a relatively non-traumatic technique, causing minimal substrate damage to occur. HWCVD also allows for low pressures that can be used for gas phase decomposition, which can be used for material etching or photo-resist removal. Because no plasma is needed in HWCVD, the substrate is decoupled from the deposition process, enabling substrates to be easily introduced and removed from the deposition chamber without disturbing the deposition. In addition, step coverage is excellent and uniformity can easily be optimized.
NREL has been working within HWCVD industry for almost 20 years and holds a number of patents, specifically in epitaxial Si growth with HWCVD. NREL researchers have found a method for producing epitaxial Si films on a substrate using HWCVD by controlling the rate of Si deposition in a temperature range that spans the transition from a monohydride to a hydrogen free Si surface in a vacuum to obtain phase-pure epitaxial Si film of increased thickness. This method produces an order of magnitude increase in both the deposition rate and achievable thickness of epitaxy by HWCVD at substrate temperatures above 570°C. Deposition rates of 110nm/min and achievable thickness of 11µm on a c-Si wafer can be produced.
Benefits- Reduces manufacturing costs
- Scalable
- Lower temperature deposition
- Rapid and controllable growth
- Control of the surface morphology during the growth
- Solar cells
- Thin-film transistors
- Light emitting diodes
- Gas sensors
- Electrochromic windows
- Organic devices
- Micromechanical structures
| Technology ID | Development Stage | Availability | Published | Last Updated |
|---|---|---|---|---|
| NREL ROIs 10-05 and 11-06 | Development | Available | 04/14/2011 | 12/20/2012 |
