Editing Quantum efficiency (section)

{{Short description|Property of photosensitive devices}}
{{distinguish|Quantum yield}}
[[Image:Quantum efficiency graph for WFPC2-en.svg|thumb|right|300px|A graph showing variation of quantum efficiency with wavelength of a CCD chip from [[Wide Field and Planetary Camera 2]], formerly installed on the [[Hubble Space Telescope]].]]
The term '''quantum efficiency''' ('''QE''') may apply to '''incident photon to converted electron''' ('''IPCE''') '''ratio'''<ref>{{cite journal|last=Shaheen|first=Sean| title=2.5% efficient organic plastic solar cells|journal=Applied Physics Letters|date=2001|volume=78|issue=6|doi=10.1063/1.1345834| url=http://apl.aip.org/resource/1/applab/v78/i6/p841_s1?bypassSSO=1| archive-url=https://archive.today/20120707154607/http://apl.aip.org/resource/1/applab/v78/i6/p841_s1?bypassSSO=1| url-status=dead|archive-date=2012-07-07| access-date=20 May 2012|bibcode=2001ApPhL..78..841S|page=841|hdl=11370/108e619e-c6c2-4cf9-859e-6f937ac027f2|hdl-access=free}}</ref> of a [[photosensitivity|photosensitive device]], or it may refer to the [[Tunnel magnetoresistance|TMR effect]] of a magnetic tunnel junction.

This article deals with the term as a measurement of a device's electrical sensitivity to light. In a [[charge-coupled device]] (CCD) or other photodetector, it is the ratio between the number of [[charge carrier]]s collected at either terminal and the number of [[photon]]s hitting the device's photoreactive surface. As a ratio, QE is dimensionless, but it is closely related to the [[responsivity]], which is expressed in [[ampere|amps]] per [[watt]]. Since the energy of a photon is [[proportionality (mathematics)#Inversely proportional|inversely proportional]] to its [[wavelength]], QE is often measured over a range of different wavelengths to characterize a device's [[efficiency]] at each photon energy level. For typical semiconductor photodetectors, QE drops to zero for photons whose energy is below the [[band gap]]. A photographic film typically has a QE of much less than 10%,<ref name=Trager200>{{cite book|last=Träger|first=Frank|title=Handbook of Lasers and Optics|date=2012|publisher=Springer|location=Berlin Heidelberg|isbn=9783642194092|pages=601, 603|url=https://books.google.com/books?id=Ad5G1HWtDRgC&pg=PA603}}</ref> while CCDs can have a QE of well over 90% at some wavelengths.