What is photovoltaic effect? Explain the principle and working of solar cell.
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 Eg of the material. This is a phenomenon in which light energy is converted into electrical energy.
⦁ 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 ≥ Eg 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