30-second summary
Applications of Photovoltaic Effect
In most photovoltaic applications, the radiation is sunlight, and the devices are called solar cells. Nowadays, solar energy is one of the most available energies in the market.
It can provide electricity to places where is no electric grid connection. Renewable energy sources are becoming more popular because the costs of PV modules have decreased in the last 5 years, and in comparison with other energy sources, it has low pollution.
Solar cells are made of materials, which are called semiconductors. PV cell generates direct current (DC) from these semiconductors when they are irradiated by photons. The common single-junction silicon solar cell can produce a maximum open-circuit voltage of approximately 0.5 volts to 0.6 volts. Solar cells are usually connected in series creating an additive voltage.
Connecting cells in parallel yields a higher current. Multiple solar cells in an integrated group, all oriented in one plane, constitute a solar photovoltaic panel or module. The typical open circuit voltage of a 300 watts solar panel should be around 39 volts, and short circuit current should be 8.33 amperes at a perfect angle and under full sunlight. Their lifetime can reach 20-30 years.
Applications of Photovoltaic Effect
In most photovoltaic applications, the radiation is sunlight, and the devices are called solar cells. Nowadays, solar energy is one of the most available energies in the market. It can provide electricity to places where is no electric grid connection. Renewable energy sources are becoming more popular because the costs of PV modules have decreased in the last 5 years, and in comparison with other energy sources, it has low pollution. Solar cells are made of materials, which are called semiconductors.
In the case of a semiconductor p–n (diode) junction solar cell, illuminating the material creates an electric current because excited electrons and the remaining holes are swept in different directions by the built-in electric field of the depletion region. PV cell generates direct current (DC) from these semiconductors when they are irradiated by photons. The common single-junction silicon solar cell can produce a maximum open-circuit voltage of approximately 0.5 volts to 0.6 volts. Solar cells are usually connected in series creating an additive voltage. Connecting cells in parallel yields a higher current. Multiple solar cells in an integrated group, all oriented in one plane, constitute a solar photovoltaic panel or module. The typical open circuit voltage of a 300 watts solar panel should be around 39 volts, and short circuit current should be 8.33 amperes at a perfect angle and under full sunlight. Their lifetime can reach 20-30 years.
Photovoltaic Effect
The photovoltaic effect is a photoelectric process that generates voltage or electric current in a photovoltaic cell when it is exposed to sunlight.
In a photovoltaic device, photons are converted into electricity. The process involves the generation of charge carriers by photon absorption, separation and transportation of the carriers, and finally their collection at electrodes.
- Photon absorption. First, photons in sunlight hit the solar panel and are absorbed by semi-conducting materials. Their energy is given to an electron in the crystal lattice. If the energy is higher than the bonding energy of the electron, the electron is freed from the bond into the conduction band, where it is free to move around within the semiconductor. This results in electron-hole pair generation.
- Charge carrier separation. The most commonly known solar cell is configured as a large-area p-n junction (semiconductor structure with built-in electric field) made from silicon. As a simplification, one can imagine bringing a layer of n-type silicon into direct contact with a layer of p-type silicon. Due to the p-n junction configuration and the materials in solar cells, the electrons are only allowed to move in a single direction. The electronic structure of the materials is very important for the process to work, and often silicon incorporating small amounts of boron or phosphorus is used in different layers. The electron is pushed by this field toward the n side and the hole toward the p side.
- Charge collection and recombination. Electrons that are created on the n-type side, “collected” by the junction and swept onto the n-type side, may travel through the wire, power the load, and continue through the wire until they reach the p-type semiconductor-metal contact. Here, they recombine with a hole that was either created as an electron-hole pair on the p-type side of the solar cell, or a hole that was swept across the junction from the n-type side after being created there. An array of solar cells converts solar energy into a usable amount of direct current (DC) electricity. The voltage measured is equal to the difference in the quasi Fermi levels of the majority carriers (electrons in the n-type portion and holes in the p-type portion) at the two terminals.