Howard Branz, front row, center, principal investigator for the team that won an R&D 100 Award for a new “black silicon” process to improve the efficiency of solar cells, poses with his National Renewable Energy Laboratory teammates at the PDIL facility. On Branz’s right is Anna Duda; on his left is Vern Yost. In the back row, left to right, are Matt Page, Scott Ward and Hao-chih Yuan. |
Natcore
Technology Inc. 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.
“Natcore
has the ability to passivate black silicon cells using their liquid
phase deposition (LPD) technology. That has been the missing piece. It’s
what will enable black silicon to reach its potential,” says Dr. Dennis
Flood, Natcore’s Chief Technology Officer.”Natcore has the ability to
passivate black silicon cells using their liquid phase deposition (LPD)
technology. That has been the missing piece. It’s what will enable black
silicon to reach its potential,” says Dr. Dennis Flood, Natcore’s Chief
Technology Officer.
“Before
Natcore’s passivation technology, it was necessary to put coated cells
into a 1,000 deg. C. furnace to create a thermal oxide,” continues
Flood. “Natcore’s LPD silica coating achieves passivation without
requiring an extra thermal process.”
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, CO. According to Flood, the result
persuaded NREL to grant Natcore a license to develop and commercialize
products based on the NREL black silicon technology.
“Double
the output, halve the cost,” says Natcore President and CEO Chuck
Provini. “That’s our mantra. To make solar cells cost-competitive, we
must reduce their cost and increase their output. The combined
NREL-Natcore technologies will reduce cost by eliminating the need for
thermal oxidation. And they’ll increase output by enabling cells to be
more productive throughout all daylight hours.”
“We’re
combining NREL’s black silicon technology with our LPD and passivation
technologies, Provini adds. “We’ll optimize the combined processes and
incorporate them into our AR-Box. AR-Box enables use of an all-liquid
phase process for creating ultralow reflectivity, high-performance
silicon solar cells at high volume production rates.” AR-Box is
Natcore’s device that uses the company’s liquid phase deposition (LPD)
process to grow antireflective (AR) coatings on silicon wafers.
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 of 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.
