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Quantum efficiency (QE) is a figure given for a photosensitive device ( charge-coupled device (CCD), for example) which is the percentage of photons hitting the photoreactive surface that will produce an electron-hole pair. It is an accurate measurement of the device's sensitivity.It is often measured on a range of different wavelengths, to characterize a device's efficiency at each energy.
QE is a very important measures for solar cells , for it gives an information on the current that a given cell will produce when illuminated by a particular wavelength. If the quantum efficiency is integrated on the whole solar spectrum, one can evaluate the current that a cell will produce when exposed to white light. The ratio between this current and the highest possible current (if the QE was 100% over the whole spectrum) gives the electrical efficiency of the solar cell. With solar cells, one often meaures the external quantum efficiency, i.e. the current obtained outside the device pro incoming photon. The quantum efficiency therefore depends of
- the absorption of light
- the collection of charges. (Once a photon has been absorbed and has generated an electron-hole pair, these charges must be separated and collected at the junction. A good-quality material is crucial to avoid charge recombination and therefore a drop in the quantum efficiency.
The spectral response is a similar measurement, but it uses different unities : A/W (Ampere/Watt) : How much current gets out of the device for an incoming light beam of a given power.
Both the quantum efficiency and the spectral response are function of the photons' wavelength : QE=QE(λ) and SR=SR(λ)
Electronics
