Scientists at Natcore Technology Inc.have created the “blackest” silicon solar cell surface ever recorded.
Scientists at Natcore Technology Inc., using simple liquid bath processes, have created a black surface on a silicon wafer with an average that reflects only 0.3% of the visible and near-infrared light that hits it, making it the “blackest” silicon solar cell surface ever recorded.
Reflectance is the proportion of light striking a surface that is reflected from it. A reflectance of 0.3% means that only 0.3% of incident light is reflected from the solar cell’s surface, while 99.7% of incident light is absorbed by the cell and is available for conversion into electrical energy.
Compared with standard production cells now available, this represents a tenfold reduction in reflectance over that portion of the spectrum, which is the source of about 80% of the usable power that can be drawn from sunlight.
The black color of black silicon results from the near-total absence of reflected light from the porous wafer surface. With solar cells, “blackness” is highly desirable because it indicates that incident light is being absorbed for conversion to energy rather than being reflected and thus wasted.
There are additional benefits to be derived from black silicon. A panel made from black silicon solar cells will produce significantly more energy on a daily basis than will a panel made from cells using the industry standard antireflective coating because it reflects less light and performs better on cloudy days and during the morning and afternoon hours when the sun hits at an angle.
Natcore representatives said its higher energy output, combined with a lower cost using the company’s patented process, could quickly make black silicon the global solar technology of choice.
“Absolute black is to reflected light as absolute zero is to heat,” says Dr. Dennis Flood, Natcore’s Chief Technology Officer. “And getting close to zero reflectance with a process that we can use for the production of commercial solar cells is simply astounding.”
Natcore’s process begins with an uncoated, textured silicon wafer with an average reflectance of approximately 8%, giving it a mottled gray appearance. First, nanoscale pores are etched into the wafer surface by submerging it for a few minutes in a liquid solution at room temperature. Next, using the company’s liquid phase deposition (LPD) process, Natcore scientists filled the pores and then over-coated them with silicon dioxide. This combination step both coated and passivated, thereby allowing lower reflectance. After the surface treatments were completed, the wafers were taken to the State of Ohio’s Photovoltaic Research and Development Center at the University of Toledo, where the reflectance was measured.
“We are already working with two equipment manufacturers to design a production tool,” said Natcore President and CEO Chuck Provini. “The tool would make 2,000 black silicon wafers per hour.”
Provini said when the design is completed, the company will begin selling the production tool. He said the company has already begun talking with potential customers in Italy, China, and India.
Page 2 of 2 - Natcore was recently granted an exclusive license by the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) to develop and commercialize a line of black silicon products based on NREL patents. Natcore’s reflectance accomplishment came about as a natural part of its work associated with that license.
“This latest achievement further strengthens our position as the sole provider of the best antireflection control technology available to silicon solar cell manufacturers,” Provini said.