Photovoltaic Power Systems

The origin of the PV potential is the difference in the chemical potential, called the Fermi level , of the electrons in the two isolated materials. When they are joined, the junction approaches a new thermodynamic equilibrium. Such equilibrium can be achieved only when the Fermi level is equal in the two materials. This occurs by the flow of electrons from one material to the other until a voltage difference is established between them, which has a potential just equal to the initial difference of the Fermi level. This potential drives the photocurrent in the PV circuit. Figure 9.2 shows the basic cell construction.