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Black Silicon Etching

Award-winning, efficient, and inexpensive photovoltaic technology

National Renewable Energy Laboratory

Contact NREL About This Technology

Three silicon wafers, showing absorbed light: (left) micron-scale texture, (center) NREL’s Black Silicon Etch, and (right) micron-scale texture with an antireflective coating.
Three silicon wafers, showing absorbed light: (left) micron-scale texture, (center) NREL’s Black Silicon Etch, and (right) micron-scale texture with an antireflective coating.

Three tilted silicon wafers, showing absorbed incident light: (left) micron-scale texture, (center) NREL’s Black Silicon Etch, and (right) micron-scale texture with an antireflective coating.
Three tilted silicon wafers, showing absorbed incident light: (left) micron-scale texture, (center) NREL’s Black Silicon Etch, and (right) micron-scale texture with an antireflective coating.

Technology Marketing Summary

The 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%.

Description

The 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
Patent 8,729,798
Patent
8,729,798
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.
05/20/2014
Issued
Patent 8,828,765
Patent
8,828,765
Forming high efficiency silicon solar cells using density-graded anti-reflection surfaces
A method (50) is provided for processing a graded-density AR silicon surface (14) to provide effective surface passivation. The method (50) includes positioning a substrate or wafer (12) with a silicon surface (14) in a reaction or processing chamber (42). The silicon surface (14) has been processed (52) to be an AR surface with a density gradient or region of black silicon. The method (50) continues with heating (54) the chamber (42) to a high temperature for both doping and surface passivation. The method (50) includes forming (58), with a dopant-containing precursor in contact with the silicon surface (14) of the substrate (12), an emitter junction (16) proximate to the silicon surface (14) by doping the substrate (12). The method (50) further includes, while the chamber is maintained at the high or raised temperature, forming (62) a passivation layer (19) on the graded-density silicon anti-reflection surface (14).
National Renewable Energy Laboratory 09/09/2014
Issued
Patent 9,034,216
Patent
9,034,216
Wet-chemical systems and methods for producing black silicon substrates
A wet-chemical method of producing a black silicon substrate. The method comprising soaking single crystalline silicon wafers in a predetermined volume of a diluted inorganic compound solution. The substrate is combined with an etchant solution that forms a uniform noble metal nanoparticle induced Black Etch of the silicon wafer, resulting in a nanoparticle that is kinetically stabilized. The method comprising combining with an etchant solution having equal volumes acetonitrile/acetic acid:hydrofluoric acid:hydrogen peroxide.
National Renewable Energy Laboratory 05/19/2015
Issued
Patent 9,076,903
Patent
9,076,903
Forming high-efficiency silicon solar cells using density-graded anti-reflection surfaces
A method (50) is provided for processing a graded-density AR silicon surface (14) to provide effective surface passivation. The method (50) includes positioning a substrate or wafer (12) with a silicon surface (14) in a reaction or processing chamber (42). The silicon surface (14) has been processed (52) to be an AR surface with a density gradient or region of black silicon. The method (50) continues with heating (54) the chamber (42) to a high temperature for both doping and surface passivation. The method (50) includes forming (58), with a dopant-containing precursor in contact with the silicon surface (14) of the substrate (12), an emitter junction (16) proximate to the silicon surface (14) by doping the substrate (12). The method (50) further includes, while the chamber is maintained at the high or raised temperature, forming (62) a passivation layer (19) on the graded-density silicon anti-reflection surface (14).
National Renewable Energy Laboratory 07/07/2015
Issued
Patent 8,815,104
Patent
8,815,104
Copper-assisted, anti-reflection etching of silicon surfaces
A method (300) for etching a silicon surface (116) to reduce reflectivity. The method (300) includes electroless deposition of copper nanoparticles about 20 nanometers in size on the silicon surface (116), with a particle-to-particle spacing of 3 to 8 nanometers. The method (300) includes positioning (310) the substrate (112) with a silicon surface (116) into a vessel (122). The vessel (122) is filled (340) with a volume of an etching solution (124) so as to cover the silicon surface (116). The etching solution (124) includes an oxidant-etchant solution (146), e.g., an aqueous solution of hydrofluoric acid and hydrogen peroxide. The silicon surface (116) is etched (350) by agitating the etching solution (124) with, for example, 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, copper nanoparticles enhance or drive the etching process.
National Renewable Energy Laboratory 08/26/2014
Issued
Application 20130340824
Application
20130340824
Efficient Black Silicon Photovoltaic Devices With Enhanced Blue Response
A photovoltaic (PV) device with improved blue response. The PV device includes a silicon substrate with an emitter layer on a light receiving side. The emitter layer has a low opant level such that it has sheet resistance of 90 to 170 ohm/sq. Anti-reflection in the PV device is provided solely by a nano-structured or black silicon surface on the light-receiving surface, through which the emitter is formed by diffusion. The nano structures of the black silicon are formed in a manner that does not result in gold or another high-recombination metal being left in the black silicon such as with metal-assisted etching using silver. The black silicon is further processed to widen these pores so as to provide larger nanostructures with lateral dimensions in the range of 65 to 150 nanometers so as to reduce surface area and also to etch away a highly doped portion of the emitter.
National Renewable Energy Laboratory 03/08/2011
Filed
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
NREL ROI's: 07-10; 09-10; 09-69; 10-69; 11-43; 12-18Development - 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. 08/02/201008/02/2010

Contact NREL About This Technology

To: Bill Hadley<Bill.Hadley@nrel.gov>