News: Scientists capture electron movements inside a solar cell

New research from the Femtosecond Spectroscopy Unit at the Okinawa Institute of Science and Technology Graduate University (OIST), published in Nature Nanotechnology, has made electron's movement measured.

"We have made a video of a very fundamental process: for the first time we are not imagining what is happening inside a solar cell, we are actually seeing it. We can now describe what we see in this time-lapse video, we no longer have to interpret data and imagine what might have happened inside a material. This is a new door to understanding the motion of electrons in semiconductors materials." Prof. Keshav Dani.

If you shine light on a material, the light energy can be absorbed by the electrons and move them from a low-energy state to a higher one. If the light pulse that you shine at the material is very, very short, a few millionths of a billionth of a second - that is a few femto seconds - it creates a very rapid change in the material. However, this change does not last long, as the material goes back to its original state on a very fast time scale. For a device to work, like in a solar cell, we have to extract energy from the material while it is still at the high energy state. Scientists want to study how materials change state and lose energy. "In reality, you cannot watch these electrons changing state on such a fast time scale. So, what you do is measure the change of reflectivity of the material," Dr. Man explained. To understand how the material changes when exposed to light, researchers expose the material to a very short, but intense, pulse of light which causes the change, and then continuing to measure the change introduced by the first pulse by probing the material with subsequent much weaker light pulses at different delay times after the first pulse.

This research provides a new insight into the movement of electrons that could potentially change the way solar cells and semiconductor devices are built. This new insight brings the technology field one step closer to building better and more efficient electronic devices.

Source
For more information:
Imaging the motion of electrons across semiconductor heterojunctions. , Nature Nanotechnology,