photovoltaic effect

Also found in: Dictionary, Thesaurus, Wikipedia.
Related to photovoltaic effect: photovoltaic cell

Photovoltaic effect

The conversion of electromagnetic radiation into electric power through absorption by a semiconducting material. Devices based on this effect serve as power sources in remote terrestrial locations and for satellites and other space applications. Photovoltaic--powered calculators and other consumer electronic products are widely available, and solar photovoltaic automobiles and aircraft have been demonstrated.

The basic requirements for the photovoltaic effect are (1) the absorption of photons through the creation of electron-hole pairs in a semiconductor; (2) the separation of the electron and hole so that their recombination is inhibited and the electric field within the semiconductor is altered; and (3) the collection of the electrons and holes, separately, by each of two current-collecting electrodes so that current can be induced to flow in a circuit external to the semiconductor itself.

There are many approaches to achieving these three requirements simultaneously. A very common approach for separating the electrons from the holes is to use a single-crystal semiconductor, for example, silicon, into which a pn junction has been diffused. Silicon is often chosen because its optical band gap permits the absorption of a substantial portion of solar photons via the generation of electron-hole pairs. The fabrication of such a device structure causes a local transfer of negative charges from the n layer into the p layer, bending the conduction and valence bands in the vicinity of the p-n boundary, and thereby creating a rectifying junction. Electrons generated in the p region can lower their energy by migrating into the n region, which they will do by a random walk process in the electric-field-free region far from the junction, or by drift induced by the electric field in the junction region. Holes created in the n region, conversely, lose energy by migrating into the p region. Thus the presence of such a junction leads to the spontaneous spatial separation of the photogenerated carriers, thereby inducing a voltage difference between current-carrying electrodes connected to the p and n regions. This process will continue until the difference in potential between the two electrodes is large enough to flatten the bands in the vicinity of the junction, canceling out the internal electric field existing there and so eliminating the source of carrier separation. The resulting voltage is termed the open-circuit voltage, and approximates the built-in voltage associated with the pn junction in the dark, a value which cannot exceed the band gap of the semiconductor. See Hole states in solids, Semiconductor, Semiconductor diode

In the limit when the device is short-circuited by the external circuit, no such buildup of potential can occur. In this case, one electron flows in the external circuit for each electron or hole which crosses the junction, that is, for each optically generated electron-hole pair which is successfully separated by the junction. The resulting current is termed the short-circuit current and, in most practical photovoltaic devices, approaches numerically the rate at which photons are being absorbed within the device. Losses can arise from the recombination of minority carriers (for example, electrons in the p-type region, holes in the n-type region) with majority carriers. See Electron-hole recombination

For a photovoltaic device to generate power, it is necessary to provide a load in the external circuit which is sufficiently resistive to avoid short-circuiting the device. In this case, the voltage will be reduced compared to the open-circuit voltage because a continuing requirement exists for carrier separation at the junction; thus some band bending and its associated internal field must be retained.

Various multiple-layered device configurations based on doped and undoped alloys of amorphous silicon have been developed for photovoltaic devices used in applications ranging from solar watches and calculators to remote power generators. The photovoltaic effect in these devices is particularly intriguing since it is possible to build up so-called tandem devices by stacking one device electrically and optically in series above another. In addition to the increased voltage and concomitant reduction in the required current-carrying capability of electrode grid structures, such devices permit, in principle, an increased efficiency of solar photovoltaic energy conversion.

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

photovoltaic effect

[¦fōd·ō·vōl′tā·ik i‚fekt]
The production of a voltage in a nonhomogeneous semiconductor, such as silicon, or at a junction between two types of material, by the absorption of light or other electromagnetic radiation.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
The Warwick team wondered if it was possible to take the semiconductors that are effective in commercial solar cells and manipulate or push them in some way so that they too could be forced into a non-centrosymmetric structure and possibly therefore also benefit from the bulk photovoltaic effect.
Hence, the photovoltaic effect means the generation of a potential difference at the junction of two different materials in response to visible light or other electromagnetic radiation.
It has been established that "anomalous photovoltaic effect" took place only in crystals where at least some stacking disorder occurred (i.e., changes in structure from ZB to WZ) [2, 3].
Photovoltaics (PV) is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect.
Solar concentrators - low-cost, prefabricated, optically efficient microlens arrays - can be placed directly over each glitter-sized cell to increase the number of photons arriving to be converted via the photovoltaic effect into electrons.
The photovoltaic effect is produced by sunlight of a particular frequency (color) causing silicon--that has been "doped" with special impurities--to give up electrons.
A solar cell produces electric current and voltage by "photovoltaic effect"--a process in which two different materials in close contact act as an electric cell when struck by light or other radiant energy.
While many of the ideas you list have merit and have been around a long time the photovoltaic effect is the closest thing to free energy that I have found and we know that PV panels are not cheap.
* 1839 Edmund Becquerel, a French physicist, observes the photovoltaic effect.
For an example, the use of the MESFET, the commonly used building block of MMICs, will be discussed as an optical input port to the GaAs chip, based on recent work.[6,7] This work discusses internal photovoltaic effect in the MESFET, which gives rise to photoresponse in the device.
Photovoltaic cell converts the luminous energy into electrical energy through the photovoltaic effect. The analysis process of this paper is based on the equivalent circuit of the photovoltaic cell of the monolithic diode model as shown in Figure 1, where [] is the photogenerated current, [I.sub.D] is diode current, [] is parallel current, IL is output current, [] is parallel resistance, Rs is series resistance, and [R.sub.L] is external load.

Full browser ?