
304 Principles of Sustainable Energy Systems
© 2008 Taylor & Francis Group, LLC
6.1.2 Photovoltaic Effect
When a photon of light is absorbed by a valence electron of an atom, the energy of the
electron is increased by the amount of energy of the photon. If the energy of the photon
is equal to or more than the band gap of these semiconductors, the electron with excess
energy will jump into the conduction band where it can move freely. If, however, the pho-
ton energy is less than the band gap, the electron will not have sufcient energy to jump
into the conduction band. In this case, the excess energy of electrons is converted to excess
kineti