ABSTRACT
Photoelectronic devices, which convert solar radiation energy into electric power, are called solar cells or photovoltaic devices. The physical processes by which photons are converted into electrical potential and current are well explained by fundamental physical theory. An utmost important issue for design of photovoltaic devices is highly efficient separation of the negative charges (electrons) from the positive ones (holes). A heterojunction could be constructed between two different semiconductors. An abrupt junction corresponds to a band edge discontinuity at the junction. Recombination loss is due to the electron–hole recombination after their being photo-excited. Semiconductors are suitable candidates for photovoltaic devices due to their unique energy band structures and doping performance. In darkness, the Fermi levels for electrons and holes in solar cells are lined up. Solar illumination breaks the original thermal dynamic balance by generating photoexcited electrons and holes in the conduction and the valence bands, respectively.
