What you Need
What to do
Take the pliers and carefully crush the black plastic away from the metal part of the diode. Start at one end and work your way along until you start to find a lump in the metal, and then start from the other end.
Connect your diode to your multimeter. Measure its Voltage and the current flowing through it. Then measure it somewhere very dark and again in full sunlight. What happens?
What may happen
You should find that in full sunlight the diode will produce a significant fraction of a volt and a few µA, but in the dark it doesn't even produce a voltage. You have made a solar cell, though not a very powerful one. Ours produced 4µW - so to power a kettle you would need 500 million of them!
Why does it happen?
A diode is often used as a one way valve for electricity, a solar cell is just a specially optimised very large diode. So any diode will work as a solar cell, though not very effectively. This is why the diode had to be covered in black plastic (otherwise it would start injecting all sorts of strange voltages into its circuit when the sun came out).
What is a Diode?
A diode is made of semiconductors such as Silicon or Germaniumm these are materials on the edge between an insulator and a conductor. Pure semiconductor doesn't conduct electricity as each atom has 4 electrons which is stable, but if you slightly increase the number of electrons these extra electrons can move around easily and conduct electricity.
They will also conduct electricity if you remove a few electrons. This is because the hole can move around like a sliding block puzzle, as the electrons move in the opposite direction. It is easiest to think of the hole as a virtual positive particle.
A diode is created by connecting a lump of N-type semiconductor to a P-type semiconductor.
If this depletion region is hit by light the energy can be used to knock an electron off an atom creating a free electron and a hole. These are pull in opposite directions and have to flow around the circuit to meet up again doing useful work.
Why is a diode a one way valve for electricity?
If you apply a voltage to the two sides of the diode depending on its direction it will have a very different effect.
Randy Heish sent us these incredible pictures of his own diode-based solar cells - powerful enough to power a clock!