Photovoltaic effect is the conversion of light energy into electrical energy. Thus, principle of obtaining power out of solar cell lies in photovoltaic effect only.Photovoltaic cells are made of semiconductors and silicon, mixed with other materials.
For Photovoltaic effect to come into existence, generally 3 main features are involved:-
- Generation of electron hole pairs in the cell
- Separation of electrons and holes at the junction
- Collection of electrons and holes at the terminals
Generation of electron hole pairs can be carried out by 3 processes:-
- Charge carrier excitation by temperature
- Charge carrier excitation by doping
- Charge carrier excitation by light
These charge carriers have to be generated at the depth lesser than the diffusion length, otherwise they cannot be collected and get recombined.Hence diffusion length limits the maximum thickness of solar cell. Photovoltaic current is generated by the minority charge carriers (electrons in p region & holes in n region) as their concentration will increase due to falling of light and this driven current is called drift current arising due to the existing electric field from n region to p region.
Along with these processes, when we incorporate losses and non idealities (arising mainly due to ohmic & metallic resistances, interface between semiconductor material and metal contact, defect states, reflection etc) in the form of resistances, an electrical model of solar cell can be prepared which can be used for further analysis.