Solar Cell

Solar cells are made using semiconductors such as silicon. Semiconductors have interesting electrical properties, making them useful for electronic devices such as the microprocessors used in computers. One of their properties is that they can be treated in different ways to become either 'positive' (p-type) or 'negative' (n-type).
Photovoltaic Cell under Illumination



Photovoltaic Cell under Illumination

A solar cell consists of two layers of semiconductor, one p-type and the other n-type, sandwiched together to form a 'pn junction'. This pn interface induces an electric field across the junction. When particles of light ('photons') are absorbed by the semiconductor, they transfer their energy to some of the semiconductor's electrons, which are then able to move about through the material. For each such negatively charged electron, a corresponding mobile positive charge, called a 'hole', is created. In an ordinary semiconductor, these electrons and holes recombine after a short time and their energy is wasted as heat.

In a solar cell, however, the electrons and holes near the pn junction are swept across in opposite directions by the action of the electric field and others diffuse towards the junction to replace them. This separation of charge induces a voltage across the device. By connecting the device to an external circuit, the electrons are able to flow - and this flow of electrons is what we call electricity.