Bismuth-based crystalline material can boost solar cell efficiency, chip design

February 20th, 2009 - 6:09 pm ICT by IANS  

Washington, Feb 20 (IANS) Physicists have discovered unusual electronic properties in a material that has potential to improve solar cell efficiency and computer chip design.
They 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.

They also discovered that diodes made from this material generate current when light falls on them, making them 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 Rutger University School of Arts and Sciences and one of the paper’s five co-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,” Cheong said.

The crystal that Cheong and his colleagues investigated is a ferroelectric material, meaning that the crystal exhibits electrical polarisation, or alignment. This polarisation, 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, said a Rutger’s release.

“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.”

These findings are scheduled for publication in Science.

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