Photovoltaic cells convert light energy into electricity at the atomic level. Although first discovered in 1839, the process of producing electric current in a solid material with the aid of sunlight wasn't truly understood for more than a hundred years. Throughout the second half of the 20th century, the principles underlying the photovoltaic effect have been determined and the manufacturing processes have been more fully refined. As a result, the cost of these devices has put them into the mainstream of modern energy producers. This was caused in part by advances in the technology - in which PV conversion efficiencies have improved considerably - an in part by improvements in manufacturing all the other components in a complete system.The conversion efficiency of a PV cell ...view middle of the document...
The "photovoltaic effect" is the basic physical process through which a PV cell converts sunlight into electricity. Sunlight is composed of photons, or particles of solar energy. These photons contain various amounts of energy corresponding to the different wavelengths of the solar spectrum. When photons strike a PV cell, they may be reflected or absorbed, or they may pass right through. Only the absorbed photons generate electricity. When this happens, the energy of the photon is transferred to an electron in an atom of the cell (which is actually a semiconductor). With its newfound energy, the electron is able to escape from its normal position associated with that atom to become part of the current in an electrical circuit. By leaving this position, the electron causes a "hole" to form. Special electrical properties of the PV cell--a built-in electric field--provide the voltage needed to drive the current through an external load (such as a light bulb).The most important parts of a solar cell are the semiconductor layers, because this is where the electron current is created. There are a number of different materials suitable for making these semi conducting layers, and each has benefits and drawbacks. Unfortunately, there is no one ideal material for all types of cells and applications. In addition to the semi conducting materials, solar cells consist of a top metallic grid or other electrical contact to collect electrons from the semiconductor and transfer them to the external load, and a back contact layer to complete the electrical circuit. Then, on top of the complete cell is typically a glass cover or other type of transparent encapsulate to seal the cell and keep weather out, and an antireflective coating to keep the cell from reflecting the light back away from the cell.
