Black Silicon Etching

Technology Marketing SummaryThe global photovoltaic (PV) industry has seen approximately 30% growth each year for the past 15 years, leading to a $10 billion industry. The PV industry is looking to lower the high costs and increase the efficiency of solar power. Scientists at NREL have designed a new process, Black Silicon Etching, that has a confirmed conversion efficiency of 16.8% in a cell without conventional antireflection coatings. This surpasses the previous black silicon record by 2.9%. Additionally, this new technology could lower the Levelized Cost Of Energy (LCOE), or the lifetime cost per unit of energy, by 2.5%.DescriptionThe winner of a 2010 R&D 100 Award, Black Silicon Etching is an innovative technology that both increases the efficiency of solar cells and decreases the capital costs of producing them. Black Silicon Etching is a one-step process using gold nanoparticle catalysis to etch nanopores into the surface of a silicon wafer, producing a density-graded black surface. The near-complete lack of reflection from the surface of the material means it can absorb more sunlight, and more electricity can be produced. Current technologies first texturize the silicon wafer and then coat the cells with an antireflective layer, which takes 8 to 30 minutes; this two-step process produces cells that reflect 3-7% of the light. NREL’s Black Silicon Etch process requires less than three minutes to complete at room temperature, and creates PV cells that absorb more than 98% of the incident light. Additionally, the cells created will have improved performance during morning, evening, and diffuse light conditions, since the black material can absorb light at incident angles which conventional cells reflect. Black Silicon Etching has been proven to be 16.8% efficient for single-crystalline silicon cells and 14.9% efficient for multi-crystalline cells, eclipsing the best previous density-graded antireflection solar cells which are 13.9% efficient.

Solar cell manufacturing is an expensive, capital-intensive process. Black Silicon Etching is a scalable technology that reduces the capital costs of PV manufacturing. This new process reduces the LCOE by 2.5% which includes $6-15 million capital savings on standard 100MW PV lines. Additionally, this novel process reduces the use of hazardous gases, can be performed with any simple wet-chemistry equipment, consumes less power and generates fewer greenhouse gases, and is easily inserted into 85% of the market’s current manufacturing processes. Black Silicon Etching could greatly improve current PV technologies by increasing the conversion efficiency and decreasing the costs of solar power while integrating smoothly into legacy manufacturing systems.Benefits

• Potential for more efficient solar cells
• Better morning, evening, and diffuse light performance
• Less expensive to produce antireflection material
• Shorter, one-step process to produce
• Easily integrated into legacy manufacturing processes
• Reduced hazardous gases, power consumption, and greenhouse gas emissions during manufacturing

Applications and Industries

• Solar cell manufacturing
• Other photovoltaic industry uses

Patents and Patent Applications

ID Number	Title and Abstract	Primary Lab	Date
Application 20090236317	ANTI-REFLECTION ETCHING OF SILICON SURFACES CATALYZED WITH IONIC METAL SOLUTIONS A method (300) for etching a silicon surface (116). The method (300) includes positioning (310) a substrate (112) with a silicon surface (116) into a vessel (122). The vessel (122) is filled (330, 340) with a volume of an etching solution (124) so as to cover the silicon surface (116). The etching solution (124) includes a catalytic solution (140) and an oxidant-etchant solution (146), e.g., an aqueous solution of hydrofluoric acid and hydrogen peroxide. The catalytic solution (140) may be a solution that provides metal-containing molecules or ionic species of catalytic metals. The silicon surface (116) is etched (350) by agitating the etching solution (124) in the vessel (122) such as with ultrasonic agitation, and the etching may include heating (360) the etching solution (124) and directing light (365) onto the silicon surface (116). During the etching, the catalytic solution (140), such as a dilute solution of chorauric acid, in the presence of the oxidant-etchant solution (146) may release metal particles such as gold or silver nanoparticles that speed or drive the etching process.	National Renewable Energy Laboratory	03/21/2008 Filed
Application 20120103825	ANTI-REFLECTIVE NANOPOROUS SILICON FOR EFFICIENT HYDROGEN PRODUCTION Exemplary embodiments are disclosed of anti-reflective nanoporous silicon for efficient hydrogen production by photoelectrolysis of water. A nanoporous black Si is disclosed as an efficient photocathode for H.sub.2 production from water splitting half-reaction.	National Renewable Energy Laboratory	10/28/2011 Filed

Technology Status

Technology ID	Development Stage	Availability	Published	Last Updated
NREL ROI's: 07-10; 07-17; 09-10; 09-69; 10-69	Development - Initial research and proof of concept is complete, though work continues to increase the efficiency closer to the maximum possible for the low measured reflection. Ongoing improvements include optimizing Black Silicon Etching for the less expensive multi-crystalline silicon cell segment of the market.	Available - Please contact the NREL Technology Transfer Office for information concerning a license to use the technology, or a partnership to further develop it.	08/02/2010	08/02/2010