MadSci Network: Physics

Re: What is the range of electromagnetic spe

Date: Thu May 27 10:29:22 1999
Posted By: Frank Berauer, Technology Transfer Engineer Microelectronics
Area of science: Physics
ID: 925522086.Ph

Hi there,

A photon (light particle) in a solar cell lifts an electron over
a "band gap" into a higher energy state. This energy can then be
used as electric current.
Obviously, a photon with less energy than the band gap cannot
lift an electron and does not contribute to the energy collected.
A photon with more energy can lift one (but only one) electron
and the energy in excess to the band gap is lost.
The most common solar cell material, Silicon, has a band gap in
the infrared region and can absorb visible, ultraviolet and higher
energy radiation.
Since the sun emits mainly near IR, visible and UV light, solar
cell performance in this region is most important.
Other materials with smaller band gaps can collect lower energy
radiation (infrared or even radio waves), but are inefficient in
the visible or higher region because more energy is lost there.
Experiments have been done with multiple layers of narrowing band
gap materials. These are much more efficient, but too expensive
for commercial applications.

Another way of collecting energy from radio waves is an antenna.
Unfortunately the amount of energy collected is so small that we
need to amplify it in order to make the radio/TV program audible.

Greetings from Batam,

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