A solar cell is a sandwich of n-type silicon (blue) and p-type silicon (red). It generates electricity by using sunlight to make electrons hop across the junction between the different flavors of silicon:
When sunlight shines on the cell, photons (light particles) bombard the upper surface.
The photons (yellow blobs) carry their energy down through the cell.
The photons give up their energy to electrons (green blobs) in the lower, p-type layer.
The electrons use this energy to jump across the barrier into the upper, n-type layer and escape out into the circuit.
Flowing around the circuit, the electrons make the lamp light up.