Photovoltaic effect

How is solar energy converted into electrical energy? The physical basis for this is simple (compare also the infobox at the beginning of this module): Electrons are released from their compound by the energy of photons (e.g. when light falls on them). This changes the distribution of the existing, negatively charged electrons, and the electric charge is created.

In a solar cell, this process looks like this (see also Figure 5): A solar cell is made up of semiconductor layers, of which one outer layer (the so-called n-layer) is negatively charged and the other outer layer (the p-layer) is positively charged (the semiconductors are made conductive beforehand by introducing foreign atoms, e.g. boron or phosphorus). The layer between the p- and n-layer is the so-called p-n junction, in which an electric field exists.

When light falls on the solar cell, the effect described above causes electrons to be released which move through the electric field in the p-n junction and thereby generate an electric voltage. The creation of the electric voltage is called the photovoltaic effect.

Figure 5: Design and function of a solar cell (Source: Kliche/Draeger 2009, p.13)