Science Buddies: "Ask an Expert"

My eleven-year-old has completed a project derived from “How Does Solar Cell Output Vary with Incident Light Intensity?” (https://www.sciencebuddies.org/science- ... p014.shtml). One of the steps involved isolating the individual wavelengths using a prism and a slot in a piece of wood, directing it at a solar cell, and then taking voltage readings of each color. Everything went great except the results are confusing and I sure can’t explain them;)

A chart of the visible light spectrum shows the red end of the scale has the lowest frequency while the purple end the highest. We assumed the higher the frequency, the greater the voltage. Yet the results are the exact opposite. Red produced the most voltage and purple the least. Amongst all we’ve tried in terms of different configurations and components, the results remained consistent.

We have had no luck finding information to support the results. We have read a multitude of articles explaining how certain frequencies have too much energy and some not enough to be converted by solar cells, but everything falls short of explaining the red = highest voltage result. Can any one offer any suggestion as to why this is happening or if this should not be happening?

Thank you.

What you are observing is how your particular solar cell absorbs different colors - i.e. frequencies - of light. When you look at your solar cell it looks a certain color. That's because that is the color of light it is reflecting back to your eyes. I have seen some solar cells that are very blue, some nearly black. Those are reflecting back the rays of light up in the violet range. They are absorbing the light in the red range.

If you are able to get solar cells that appear to be different colors, you should be able to see a difference in the color of light that produces the most voltage.

Thanks for your response. These particular cells definitely have a bluish tint to them so that makes sense.