The U.S. Department of Energy's National Renewable Energy Laboratory (NREL) has granted Natcore Technology a patent license agreement for developing and commercializing black silicon products. NREL and Natcore also intend to sign a cooperative research and development agreement for the development of commercial prototypes of NREL's black silicon inventions.
After a silicon wafer is etched with nano-scale pores its surface gets an apparent black color, due to the lack of reflected light from the surface of the porous wafers. In black silicon, reflectance and the angular dependence of the reflectance is lower than that from the cell panels made with standard thin film coating. A black silicon panel hence performs better when the sun hits it at an angle and also on cloudy days. The panel thus produces a greater amount of energy at a lower cost than the standard cell panels.
Solar cells desire low reflectivity, as reflected sunlight is wasted. A polished silicon wafer surface has a reflectivity of nearly 40%. Providing antireflective coating reduces the reflectivity to around 6%. The black silicon process has the capability to reduce the average reflectivity to a value lower than 1.5%.
A major hindrance in converting the increased absorption of light into more power output has been the increased area of silicon that is exposed on the mesas atop the wafer surface and on the pore sidewalls. Passivation or treating the area from trapping the electric charges generated by the light when they move towards the solar contact cells has to be done. Natcore possesses liquid phase deposition (LPD) technology, which can passivate black silicon cells. This technology also avoids the need of an additional thermal oxidation process.
The President and CEO of Natcore, Chuck Provini, stated that reducing the cost and increasing the output will make the solar cells cost-competitive. Combining and optimizing the LPD, passivation and black silicon technology in Natcore’s AR-Box will help produce silicon solar cells with ultralow reflectivity at high volumes.
Natcore has received exclusivity in diffused emitters that have liquid phase passivation through the patent agreement. The NREL license includes a royalty structure, development and commercialization plans and technical milestones.