How To Build A Solar Cell
Here are step by step instructions for your DIY solar cell project
More About Solar Cells
Before starting to build a solar cell, it might be worth reading about the effeciency, longevity and cost rational for homemade solar cells.
Clue: It is NOT motivated at all from a cost perspective to make your own solar cell.
If you still want to build a solar cell, you'll get detailed instructions below. Of course it can be a fun project ot carry out even if it won't make you rich...
Step By Step Instructions To Build A Solar Cell
- One sheet of copper flashing from a hardware store. Cost: Approximately $5.00 per square foot. You will need about half a square foot to build a solar cell.
- Two alligator clip leads.
- A sensitive micro-ammeter that can read currents between 10 and 50 microamperes.
- An electric stove. If your stove is gas you can buy a small one-burner electric hotplate. You will need one rated at 1100 watts or higher so the burner gets red-hot.
- A large clear plastic bottle. You will need to cut off the top of the bottle. A 2 liter spring water bottle or a large mouth glass jar work quite well.
- Table salt.
- Tap water.
- Sand paper or a wire brush attached to an electric drill.
- Sheet metal shears to cut the copper sheeting.
- Cut a piece of the copper sheeting that is about the size of the burner of your stove or hotplate.
- Wash your hands. It is important your hands are clean and have no trace of grease or oil on them.
- Wash the copper sheet with soap or cleanser to remove any oil or grease on it.
- Use sandpaper or the wire brush to thoroughly clean the copper sheeting to remove any sulphide or other light corrosion.
Place the clean, dry piece of copper sheet on the burner and turn the burner to its highest setting.
Note: As the copper starts to get hot, beautiful oxidation patterns begin to form when you build a solar cell. You will see a variety of colors emerge and cover the copper including oranges, purples, and reds. As you continue heating the copper the colors are replaced with a coating of black cupric oxide. This is not the oxide you need. It will flake off later, revealing the reds, oranges, pinks, and purples of the cuprous oxide layer underneath.
- Let the copper cook for a half an hour to ensure the black coating will be thick.
Note: This is important, since a thick coating will flake off nicely, while a thin coat will stick to the copper.
- Turn off the burner when you have completed "cooking" the copper for 30 minutes.
Leave the hot copper on the burner to cool. If you cool it too quickly, the black oxide will stay stuck to the copper so take your time and don't rush the process.
Note: The copper shrinks as it cools. The black cupric oxide also shrinks but they shrink at different rates, which makes the black cupric oxide flake off. The little black flakes usually pop off the copper with a strong enough force to make them fly a few inches. Be prepared for a little more cleaning around the stove.
- When the copper has cooled to room temperature (this takes about 20 minutes), most of the black oxide will have flaked off. You can do a light scrub of the copper with your hands under running water. That will remove most of the remaining small bits of the black. Resist the temptation to remove all of the black spots by hard scrubbing or by flexing the soft copper. This can damage the delicate red cuprous oxide layer you need to make the solar cell work.
- Cut another sheet of copper about the same size as the first one. Bend both pieces gently, so they will flex and fit into the plastic bottle or jar without touching one another. The cuprous oxide coating that was facing up on the burner is usually the best side to face outwards in the jar, because it has the smoothest, cleanest surface.
- Attach the two alligator clip leads, one to the new copper plate, and one to the cuprous oxide coated plate. Connect the lead from the clean copper plate to the positive terminal of the meter. Connect the lead from the cuprous oxide plate to the negative terminal of the meter.
- Mix a couple tablespoons of salt into some hot tap water. Stir the mixture until all the salt is dissolved. Carefully pour the saltwater into the jar, but do not get the clip leads wet. The saltwater should not completely cover the plates -- you should leave about an inch of plate above the water, so you can move the solar cell around without getting the clip leads wet.
- Place the solar cell in the sun and measure the current. When you build a solar cell, the homemade cells can generate up to about 50 micramps of power.
Note: The solar cell is a battery, so even in the dark, it will usually show a few microamps of current.
How does it do that? Cuprous oxide is a semiconducting material. A semiconductor has properties that lie somewhere in between a conductive material where electricity can flow freely, and an insulating material which binds electrons tightly to their atoms and does not allow any free flow of electrons.
In a semiconductor, there is a hole, called a bandgap between the electrons that are bound tightly to the atom, and the electrons that are farther away from the atom. In the bandgap electrons can move freely and conduct electricity. Electrons cannot however, stay inside the bandgap. An electron cannot gain just a little bit of energy and move away from the atom's nucleus into the bandgap. An electron must gain enough energy to move farther away from the nucleus, outside of the bandgap. Similarly, an electron outside the bandgap cannot lose a little bit of energy and fall just a little bit closer to the nucleus. It must lose enough energy to fall past the bandgap into the area where electrons are allowed.
When sunlight hits the electrons in the cuprous oxide, some of the electrons gain enough energy from the sunlight to jump past the bandgap and become free to conduct electricity.
The free electrons move into the saltwater, then into the clean copper plate, into the wire, through the meter, and back to the cuprous oxide plate.
As the electrons move through the meter, they perform the "work" or provide the energy required to move the needle. When darkness or a shadow falls on the solar cell, there are fewer electrons available to move through the meter so the needle dips back down and less current is produced.
If you want to see how a solar cell can be made, have a look at this video clip, where the instructor will build a solar cell similar to ours above.
Instructions: When watching the video clips, start the videos by clicking the small arrow down to the left, not the large one in the middle of the screen. If you're using Internet Explorer and your browser and the video doesn't start, try clicking twice on the small arrow.
More About Solar Cells
Want to try other DIY solar projects? Have a look at the list to the right for more inspiration.
Once you're done with the project to build a solar cell or with some other solar DIY project, please take a moment to brag about it here.
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