Nano particles are incorporated into various layers of thin film solar cells. near field enhancement is one way of increasing the photon absorption in the active layer. Can anybody explain to me or recommend to me a good reference which explain the mechanism of increasing absorption due to near field enhancement?
Dear Shehan,
This is a very inter-sting question. Metal nanoparticles embeded into semiconductors are used to enhance the absorption of light near the energy gap especially for indirect gap semiconductors. Nonoparicles can absorbed light in their surface plasmons. These excited plasmons have strong near field leading to a generation of electron hole pairs. The other mechanism of effect is that the nano metallic Particles scatter the incident optical rays when arranged in a periodic form that can form together with the back metallization a multiple reflection light traps increasing the path of the light into the m aerial and increasing the probability of absorbing the photons. The third mechanism is Light trapping by the excitation of surface plasmon polaritons at the metal/semiconductor interface. A corrugated metal back surface couples light to surface plasmon polariton or photonic modes that propagate in the plane of the semiconductor layer.
Please for more information please follow the paper in the Link:http://www.nature.com/nmat/journal/v9/n3/pdf/nmat2629.pdf
You will find it really very useful it explains the mechanisms by which nano metal particles enhance the light absorption in the solar cells and heps reducing the thinness of the active material.
However some of the optical energy absorbed by the nanoparticle will be lost as ohmic losses.
wish you success
Dear Abdelhalim Zekry
Thank you very much for your reply. However I am more interested in the physics (or mechanism) of how this strong near field due to excited plasmons generates electron hole pairs in the semiconductor.
Dear Shehan,
i would expect that the strong field means that it is strong enough to torn out valence electrons from their valence bond similar to the phenomena of field emission.
Basically he valence electrons can be made free by the mechanisms:
- Thermal emission by heat,-
-photo emission by photons of suitable light
-Field emission by increasing the the electric field such that it can break the electron bond
- secondary electron emission as happens in the avalanche breakdown. where accelerated particles electrons or holes can knock out valence electrons from the valence band to conduction band.
wish you success.
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