A solar cell is basically a p-n junction which generates emf when solar radiation falls on the p-n junction.
It works on the same principle (photovoltaic effect) as the photodiode, except that no external bias is applied and the junction area is kept much larger for solar radiation to be incident because we are interested in more power. A simple p-n junction solar cell is shown in Fig.
The generation of emf by a solar cell, when light falls on, it is due to the following three basic processes: generation, separation and collection:
- Generation of e-h pairs due to light (with hν > Eg ) close to the junction;
- Separation of electrons and holes due to the electric field of the depletion region. Electrons are swept to n-side and holes to p-side;
- The electrons reaching the n-side are collected by the front contact and holes reaching p-side are collected by the back contact. Thus p-side becomes positive and n-side becomes negative giving rise to photovoltage.