Most thermocouples that I've seen being sold online consist of two separate metal wires connected at junctions. Many smaller thermoelectric generators consist of a combination of iron and copper or iron and aluminum. However, I'm a tad confused why two different materials are being used.
If I take a look at the image below, I see that an n-type and p-type semiconductor is attached to a conducting wire with a heat source and heat sink on opposite ends. Do the semiconductor materials need to be different? For instance, can't I simply use n-type and p-type doped germanium? Why do I need to use two distinct metals? Is there a benefit, for instance using silicon for one and germanium for the other?
Does the circuit wire need to be a special alloy, or just regular copper wire to transfer current?
Ultimately, I'm a bit confused regarding the Seebeck Effect. I've seen this diagram, but also models with different alloys. Any clarification will be great!