Natcore Technology has been granted a patent license agreement from the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) to develop and commercialize a line of black silicon products — including equipment, chemicals, and solar cells — based on NREL patents. The license grants Natcore exclusivity in the field of diffused emitters with liquid phase passivation.
Natcore and NREL have also agreed to enter into a Cooperative Research and Development Agreement to develop commercial prototypes that embody NREL’s black silicon inventions.
“Black silicon” refers to the apparent color of the surface of a silicon wafer after it has been etched with nano-scale pores; the black color results from the absence of reflected light from the porous wafer surface. R&D Magazine awarded the black silicon technology an R&D 100 Award in 2010, identifying it as one of the top 100 technological innovations of the year.
A panel made from black silicon solar cells will produce a significantly greater amount of energy (KwHrs) on a daily basis than will a panel made from cells using the industry standard thin film coating, not only because the reflectance is lower but also because the angular dependence of the reflectance from black silicon is much lower as well. The latter fact means a black silicon panel will perform better during the morning and afternoon hours when the sun hits at an angle and will also outperform standard cell panels on cloudy days. The combination of lower cost and higher energy output per kilowatt of installed array peak power should quickly make black silicon the antireflection control technology of choice in the industry.
For solar cells, minimum reflectivity is desirable because sunlight that is reflected, rather than absorbed, is wasted. The reflectivity of a polished silicon wafer surface approaches 40%, giving the wafer its shiny appearance. Adding the industry’s typical antireflective coating reduces the average reflectivity to approximately 6% and gives the cells their distinctive dark blue color. The black silicon process has been shown by Natcore scientists and NREL researchers to reduce average reflectivity to less than 1.5%.
Black silicon solar cells have been studied since the 1980s because of their potential for significantly improved performance compared to standard production cells. But a key obstacle to turning their increased light absorption into increased power output is a significantly increased area of exposed silicon on the sidewalls of the pores and on the small mesas that remain at the top surface of the wafer itself. This increased area must be passivated, or treated to keep it from trapping the light-generated electric charges as they migrate toward the contacts of the solar cell, a process that robs the cell of output power.
Prior to today’s announcement, NREL sent black silicon wafers with junctions — unfinished cells — to Natcore. Natcore coated them with SiO2 and passivated them. NREL then applied contacts and tested the completed cells in their labs in Golden, Colo. The result persuaded NREL to grant Natcore a license to develop and commercialize products based on the NREL black silicon technology.
The NREL license contains a development and commercialization plan that establishes technical and market milestones for Natcore, along with a royalty structure. These are subject to confidentiality provisions set by the parties. The technical milestones include solar cell efficiency goals, some of which are to be met by August 2012. The market milestones include commercial sale dates and dollar targets. The agreement is dated December 12, 2011, and is effective for as long as the NREL patents are enforceable.
NREL is the U.S. Department of Energy’s primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for DOE by the Alliance for Sustainable Energy LLC.