For photovoltaic power generation, pn junction is the core unit. The electric field in the junction can separate and transport the electron and the hole to negative and positive electrodes, respectively. Once the pn junction is connected with a load and exposed to a light ray, it can convert photon power into electrical power and deliver this power to the load. This photovoltaic application has long been used as the power supply for satellites and space vehicles, and also as the power supply for renewable green energy.
