Rutgers Physicists Find Unusual Electronic Properties in Materials That May Improve Solar Cells, Computer Chips

Rutgers Physicists Find Unusual Electronic Properties in Materials That May Improve Solar Cells, Computer Chips

NEW BRUNSWICK, N.J. – Physicists at Rutgers University
have discovered unusual electronic properties in a material that has potential
to improve solar cell efficiency and computer chip design.

The scientists determined that a crystal made of bismuth,
iron and oxygen can perform an electronic feat typically not feasible with
conventional semiconductors. It acts as a reversible diode – essentially an
electronic turnstile that lets current flow in one direction under certain
conditions and in the opposite direction under different conditions.  Traditional semiconductor diodes are not
reversible – the direction of current flow that they allow is fixed during
fabrication.

The researchers reported their findings today in a paper
published in Science Express, an advance web posting of papers to be published
in upcoming issues of the journal Science.

The scientists also discovered that diodes made from this
material generate current when light falls on them, making the material a
potential candidate for future solar cells. The material appears very sensitive
to light at the blue end of the spectrum, a property that has the potential to
increase solar cell efficiency.

“We’ve reached the upper limit of efficiency with today’s
solar cells,” said Sang-Wook Cheong, physics professor in the School of Arts
and Sciences and one of the paper’s five authors. “While we still don’t know
how efficiently this material will ultimately perform as a solar cell, we do
need to keep investigating alternate technologies that show potential for
improvement.”

The crystal that Cheong and his colleagues investigated is a
ferroelectric material, meaning that the crystal exhibits electrical
polarization, or alignment. This polarization, which the scientists believe
controls the crystal’s ability to act as a diode, is known as a “bulk effect” –
a characteristic that permeates the whole crystal. In contrast, traditional
semiconductors act as diodes based on electrical effects at the interfaces
between two different materials.

By applying an external voltage on the ferroelectric
crystal, the polarization of the material reverses, along with the direction
that the diode allows electricity to flow.

“This could make computer chip designs more flexible,” said
Cheong. “Engineers could design a single circuit element that performs one task
under a certain configuration and another task under a different
configuration.”

The material belongs to class of crystalline materials known
as perovskites, which have two positive ions of very different atomic sizes (in
this case, bismuth and iron) bound to negative ions (in this case, oxygen). It
has three oxygen atoms for each bismuth and iron atom.

Co-authors of the Science paper are Rutgers
postdoctoral research fellow Taekjib Choi, graduate student Young Jai Choi, and
associate professor Valery Kiryukhin. Another co-author, SeongSu Lee, was a Rutgers postdoctoral research fellow and is now at the
Korea Atomic Energy Research Institute.

The National Science Foundation funded the research. Taekjib
Choi was partially supported by a Korea Research Foundation Grant funded by the
Korean government.

Media Contact: Carl Blesch
732-932-7084, ext. 616
E-mail: cblesch@ur.rutgers.edu