PHOTOVOLTAIC EFFECT:-

• In photoelectric effect when radiation is incident on a metal surface electron are ejected. In photovoltaic effect, certain materials being exposed to radiation generates electron hole pairs available for conduction. As a result a voltage is developed across the material. The radiation energy E= hϑ is required to be greater then the band gap energy E_g of the material. This is a phenomenon in which light energy is converted into electrical energy.

SOLAR CELL.

• Solar cell is a semiconductor device that converts solar energy into electrical energy. This is a p-n junction diode with very doping level. Solar cells have a flat shape with a very thin top layer. So that the incident solar energy can reach the junction area.
• As the solar radiation is incident on the device due to the radiation energy $E=hϑ ≥E_g$ electron hole pairs are generated in p and n region.
• In the energy band structure of the solar cell in fig it is seen that the conduction band is lower in the region than that in the p region. Hence , the generated electrons of the conduction band of p region travel to the conduction band of n region which is at a lower electron energy level. Similarly the holes created in the valence band of the n region move to the valence band of the p region at a lower hole energy level.

• This diffusion of electrons and holes through the junction constitutes the current .

• The top surface of the solar cell is coated with an antireflection film to maximize the utilization of the incident solar energy by the junction .

• A solar cell does not need a power supply. It generates power.

• Materials used for solar cell are different types pf semiconductor, single crystal , polycrystal, thin silicon wafers etc