Researchers in
Assistant Professor Yi Cui's lab (from left, graduate students Vijay
Narasimhan,
Ruby Lai and
Thomas Hymel) have discovered how to make the metal contacts on the surface
of solar cells
nearly invisible to incoming light. The new technique could significantly
improve
solar-cell
efficiency. (Mark Shwartz / Precourt Institute for Energy)
(November 25, 2015) Stanford
scientists have discovered how to make the electrical wiring on top of solar
cells nearly invisible to incoming light. The new design, which uses silicon
nanopillars to hide the wires, could dramatically boost solar-cell efficiency.
A solar cell is basically a semiconductor, which converts
sunlight into electricity, sandwiched between metal contacts that carry the
electrical current.
But this widely used design has a flaw: The critical but
shiny metal on top of the cell reflects sunlight away from the semiconductor
where electricity is produced, reducing the cell's efficiency.
Now, Stanford scientists have discovered how to hide the
reflective upper contact and funnel light directly to the semiconductor below.
Their findings, published in the journal ACS Nano, could lead to a new paradigm
in the design and fabrication of solar cells.
"Using nanotechnology, we have developed a novel way to
make the upper metal contact nearly invisible to incoming light," said
study lead author Vijay Narasimhan, who conducted the work as a graduate
student at Stanford. "Our new technique could significantly improve the
efficiency and thereby lower the cost of solar cells."
Mirror-like metal
In most solar cells, the upper contact consists of a metal
wire grid that carries electricity to or from the device. But these wires also
act like a mirror and prevent sunlight from reaching the semiconductor, which
is usually made of silicon.
"The more metal you have on the surface, the more light
you block," said study co-author Yi Cui, an associate professor of
materials science and engineering.
"That light is then lost and cannot be converted to
electricity."