The photovoltaic effect Cynthia M. Rollins The photovoltaic effect

Topics What is the photovoltaic effect? Some history How the photovoltaic effect works? Anatomy of a solar cell

What is the photovoltaic effect Photovoltaic’s is the direct conversion of light into electricity at the atomic level.

History In 1839, Alexandre Edmond Becquerel observed the photoelectric effect via an electrode in a conductive solution exposed to light. In 1887, Heinrich Hertz observed the photoelectric effect and the production and reception of electromagnetic (EM) waves. In 1902, Philipp Eduard Anton von Lenard observed the variation in electron energy with light frequency Albert Einstein's mathematical description in 1905 of how the photoelectric effect was caused by absorption of quanta of light.

How the photovoltaic effect Works Sunlight is composed of photons (the amount of energy in a photon being proportional to the frequency of its light). When photons strike a solar cell, the vast majority are either reflected or absorbed (some really high-energy photons will blow right through, but they're of no concern here). Sunlight is composed of photons, or "packets" of energy. When photons strike a solar cell, the vast majority are either reflected or absorbed

How the photovoltaic effect Works When a photon is absorbed, its energy is transferred to the semiconductor electron escapes from its normal position associated with that atom. The electron causes a hole to form. Each photon with enough energy will normally free exactly one electron, and one hole. Note that both electrons and holes are mobile, and as such can be current carriers. At the atomic level, semiconductors are crystals that in their pure state are resistive, but when the proper impurities are added (this process is called doping) in trace amounts (often measured in parts per billion), display much lower resistance along with other interesting and useful properties. Depending on the selection of impurities added, semiconductor material of two electrically-different types can be created -- one that is electron-rich (called N-type, where N stands for Negative), or one that is electron-poor (called P-type, where P stands for Positive). When a photon is absorbed, its energy is transferred to the semiconductor in particular, to an electron in an atom of the cell. If enough energy is transferred, the electron can escape from its normal position associated with that atom In the process the electron causes a hole (i.e., an empty spot where the electron used to be)

How the photovoltaic effect Works

Anatomy of a solar cell

Topics covered What is the photovoltaic effect Brief history How photovoltaic effect Work Quantum level How to calculate the energy of a photon Basic anatomy of a solar cell

http://science.nasa.gov/headlines/y2002/solarcells.htm http://en.wikipedia.org/wiki/Energy_use_in_the_United_States http://www.solarbotics.net/starting/200202_solar_cells/200202_solar_cell_physics.html http://science.howstuffworks.com/solar-cell3.htm http://en.wikipedia.org/wiki/Photovoltaic_effect#History