Photovoltaic cells

Hello! Sylvia here:) 

Solar photovoltaic energy conversion is a one-step conversion process which generates electrical energy from light energy. The explanation relies on ideas from quantum theory. Light is made up of packets of energy called photons, whose energy only depends upon the frequency, or colour of the light. The energy of visible photons is sufficient to excite electrons, bound to solids, up to higher energy levels where they are more free to move. Normally when light is absorbed by matter, photons are given up to excite electrons to higher energy states within the materials, but the excited electrons quickly relax back to their ground state.

In a photovoltaic device, however, there is some built-in-asymmetry which pulls the excited electrons away before they can relax, and feeds them to an external circuit. The extra energy of the excited electrons generate a potential difference, or electromotive force(e.m.f). This force drives the electrons through a load in the external circuit to do electrical work.

The effectiveness of a photovoltaic device depends upon the choice of light absorbing materials and the way in which they are connected to the external circuit.

The solar cell is the basic building block of solar photovoltaics. The cell can be considered as a two terminal device which conducts like a diode in the dark and generates a photovoltage when charged by the sun. Usually it is a thin slice of semi conductor material. The surace is used to reflect as little visible light as possible and appears dark blue or black. A pattern of metal contacts is imprinted on the surface to make electrical contact.