Continuing our educational posts, today we’ll talk about the cute little solar cells in our blinky awesomeness. Cause, how do they work anyway? And why are they called a cell, are they in jail?
A solar cell functions the opposite of an LED (check out our LED post). And if that wasn’t cool enough, some LED’s can work both ways, emitting light AND absorbing light to generate electricity. Whoa, intense! But that is a post for another day. Wikipedia has a really comprehensive entry on solar cells, for those who want more technical jargon.
Inside those tiny solar cells (cell as in plant or animal cell, not jail) are Silicon alloys. Based on their structure the Silicon alloys are either called P-type or N-type. Just as with the LED, N-type has an excess of electrons and P-type is missing electrons. Put these two types next to each other in a sandwich and you have the beginning of a solar cell. But it wouldn’t be as tasty as a plant and animal cell sandwich. Hmmm, sandwich.
Light to the rescue!
Ok, back on track. The electrons in the N-type silicone want to flow into the P-type silicone, but they need a little push. This is where light comes to the rescue, striking the N-type Silicone and giving the electrons that little push of energy. Conductors on top and bottom of the solar cell sandwich capture the electrons and they flow around the circuit. Vola, light into electricity!
Hungry for more than the sun.
Although they are called “solar” cells, it is a bit of a misnomer. Solar cells can actually produce electricity from many light sources. Scientists design the solar cell for different light sources, to get better efficiency depending on their application. Two of the more common types of solar cells are called amorphous (α-Si) and crystalline (c-Si). The words amorphous and crystalline refer to the structure of the silicon on the molecular level. Again, refer to Wikipedia if you want more detail. What these two categories mean on a practical level is they prefer different light spectrums. Not everyone likes the same sandwich, I like grilled cheese, you may like roast beef. We both still get fed.
The graph below is from Amortron’s website, please forgive the label on the green line. We think the awkward wording “luminous level of human beings” is due to a poor translation. The green line shows what wavelengths of light the human eye can detect. Notice that the light blue line for white fluorescent light (office lighting and the new compact high efficiency lighting) overlaps nicely with the red line for amorphous Si. However the dark blue line for crystalline Si solar cells does NOT overlap well with fluorescent lighting. Lumen jewelry uses both amorphous and crystalline solar cells, so some of them work well with indoor lighting and others do not. Have fun figuring it out!