A flat device for converting solar radiation into direct electric current. A photovoltaic (or solar) cell is essentially a pair of semiconductors connected by a p-n junction. When photons hit the surface, they release electrons from the crystal lattice, which accumulate in the n-layer. This creates a voltage between the electrode connected to the n-layer and the electrode connected to the p-layer; this potential can be used to create current. Cells are connected in parallel or in series into solar panels. The most common material used to make photovoltaic cells is silicon. There are monocrystalline, polycrystalline and thin film solar cells.