There are 2 kinds of dopant. In a silicon crystal, each atom has 4 valence electrons, which are shared with a neighboring atom to form a stable tetrahedral structure. Phosphorus, which has 5 valence electrons, is a donor and causes extra electrons to appear in the conduction band. This reverse field plays a vital part in the functioning of the device. In the crystalline silicon, electron-hole generation takes place throughout the thickness of the cell, in concentrations depending on the irradiance and the spectral composition of the light.
Photon energy is inversely proportional to wavelength.
Most are absorbed within a thickness of 100 m. The electrons and holes diffuse through the crystal in an effort to produce an even distribution. Some recombine after a lifetime of the order of one millisecond, neutralizing their charges and giving up energy in the form of heat. Others reach the junction before their lifetime has expired. If the cell is connected to a load, electrons will be pushed from the negative contact through the load to the positive contact, where they will recombine with holes.