Black Silicon
Natcore has an exclusive patent license 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. Natcore’s exclusivity covers the field of diffused emitters with liquid phase passivation.
“Black silicon” refers to the apparent color of the surface of a silicon wafer after it has been etched with nano-scale pores. The etching takes place in a matter of a few minutes in a liquid solution at room temperature; the black color is not a color at all but results from the absence of reflected light from the porous wafer surface.
The reflectivity of a polished silicon wafer surface approaches 40%, giving the wafer its shiny appearance. Adding the typical solar cell industry 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 researchers at NREL to further reduce the average reflectivity to less than 1.5%.
A key impediment to turning a solar cell’s increased light absorption into increased power output, however, 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.
Passivation is the process of filling the dangling atomic bonds at the surface of the solar cell, as well as reducing the numbers of defects that always exist in the upper region of the cell body. It is critical to enabling production of long-term, high-performance silicon solar cells.
In September 2010, Natcore scientists announced their success in passivating standard commercial silicon solar cells on which a silica film had been grown using our liquid phase deposition (LPD) process. While it is likely that a thermal oxidation process could also accomplish the passivation of black silicon, that would be costly. Furthermore, it’s not practical for implementation in a high-volume solar cell fabrication line. The ability of Natcore’s LPD process to passivate black silicon eliminates the need for thermal oxidation. It also enables use of an all-liquid phase process for creating ultralow reflectivity, high-performance silicon solar cells at high volume production rates. That translates to lower cost than is possible with current solar cell manufacturing technology.
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.
Natcore-sponsored research, conducted by Professor Andrew Barron’s group in combination with research by Natcore scientists working at the Ohio State University, resulted in a 20-fold increase in a parameter called minority carrier lifetime for the LPD-coated black silicon, compared to the uncoated black silicon surface. According to research by NREL, such a result would enable the power gains promised by using black silicon for solar cell manufacturing to actually be realized.
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.
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.
“Black silicon” refers to the apparent color of the surface of a silicon wafer after it has been etched with nano-scale pores. The etching takes place in a matter of a few minutes in a liquid solution at room temperature; the black color is not a color at all but results from the absence of reflected light from the porous wafer surface.
The reflectivity of a polished silicon wafer surface approaches 40%, giving the wafer its shiny appearance. Adding the typical solar cell industry 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 researchers at NREL to further reduce the average reflectivity to less than 1.5%.
A key impediment to turning a solar cell’s increased light absorption into increased power output, however, 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.
Passivation is the process of filling the dangling atomic bonds at the surface of the solar cell, as well as reducing the numbers of defects that always exist in the upper region of the cell body. It is critical to enabling production of long-term, high-performance silicon solar cells.
In September 2010, Natcore scientists announced their success in passivating standard commercial silicon solar cells on which a silica film had been grown using our liquid phase deposition (LPD) process. While it is likely that a thermal oxidation process could also accomplish the passivation of black silicon, that would be costly. Furthermore, it’s not practical for implementation in a high-volume solar cell fabrication line. The ability of Natcore’s LPD process to passivate black silicon eliminates the need for thermal oxidation. It also enables use of an all-liquid phase process for creating ultralow reflectivity, high-performance silicon solar cells at high volume production rates. That translates to lower cost than is possible with current solar cell manufacturing technology.
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.
Natcore-sponsored research, conducted by Professor Andrew Barron’s group in combination with research by Natcore scientists working at the Ohio State University, resulted in a 20-fold increase in a parameter called minority carrier lifetime for the LPD-coated black silicon, compared to the uncoated black silicon surface. According to research by NREL, such a result would enable the power gains promised by using black silicon for solar cell manufacturing to actually be realized.
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.
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.
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