Normally solar panel is composed of solar cells, EVA, PCB, PET or glass. The main element to make solar panel work is solar cells. Solar cell means Photovoltaic cells. There are two layers of silicone on this photovoltaic cell. One layer mixed with boron is N-type layer. The other layer mixed with arsenic is P-type layer. When sunlight hits N-type layer, the free electrons will be excited. And since N-type layer is very close to P-type layer, the free electrons will go through the boundary between two layers and create current. Then the circuit is built up.
But because the solar cells are very fragile, so we need to encapsulated together with PCB EVA and PET or glass. Even solar panels can generate electricity, but it can not keep this electricity inside all the time, that is why we need to connect solar panel with other storable devices, like battery, power bank and so on.
The power generated by solar panels is depending on the size of solar panel. Taking calculator for example, it needs small current, so small size solar panel is enough to make it working. But if you want to charge an iphone 6 fully within 3-4hours, you need a 12W solar panel at least.