what is quantum theory and quantum efficiency??
Answers
Answer:
The "quantum efficiency" (Q.E.) is the ratio of the number of carriers collected by the solar cell to the number of photons of a given energy incident on the solar cell. ... Quantum efficiency is usually not measured much below 350 nm as the power from the AM1. 5 contained in such low wavelengths is low.
Explanation:
This is indeed a confusing subject, especially that depending on the field (photoluminescence, photochemistry, photovoltaics), the definitions may vary.
From the photophysical point of view, one definition is clearly established:
the quantum yield is the ratio of the number of emitted photons to the number of absorbed photons.
This concept can be broadened to accomodate other phenomena (e.g. in photochemistry): number of events/number of absorbed photons
In photoluminescence, the quantum yield reflects the ratio of radiative transitions to the sum of radiative and nonradiative transitions, expressed with the rate constants: k(r)/[k(r)+k(nr)]
A subtle distinction can be made: the above defined quantum yield is sometimes referred to as "internal quantum yield, iQY", whereas the "external quantum yield, eQY" then refers to the number of photons impinging on the sample. This quantity is always smaller (or at most equal) to the internal quantum yield. A compound with high iQY but with low absorbance will have a small eQY
Efficiencies (Greek letter eta) in principle refer to energy, but they are also defined differently (see below):
quantum efficiency = energy output/energy input
It is only equal to the quantum yield if the photoluminescent system is a 2-level system and if there is no nonradiative process.
As for QY, QE can be defined as internal or external. For instance in solar cells:
iQE = number of electrons produced/number of absorbed photons
eQE = number of electrons produced/number of incident photons
The important point when reporting QY or QE data is to always define exactly what is meant.
Hope it helps....
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