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I Transmittance and Absorbtion of light

  1. May 22, 2016 #1
    I'm trying to understand the graph (attached) and if 'Z' is the absorptance or transmittance of amorphous silicon or CiGS, or the absorptance of ZnO.

    The bandgap of CiGs is between 1.1eV and 1.7eV.

    ZnO has a bandgap of 3.3eV, so any photon energy below that will not be absorbed. The 'Z' part of the graph doesn't trend upward after 3.3 either, so I don't think 'Z' is the absorptance of ZnO. That leaves amorphous silicon and CiGs.

    I found this info (below) on PVEducation. It makes me think that the answer is the absorptance of CiGs, because 'Z' increases around the 1.1eV and 1.7eV values, and above 1.7eV, the energy of the photon is > energy of the bandgap. It couldn't be the transmittance of CiGs because it wouldn't be so high around 1.1eV to 1.7eV. It would be low, no?
    • Eph < EG Photons with energy Eph less than the band gap energy EG interact only weakly with the semiconductor, passing through it as if it were transparent.
    • Eph = EG have just enough energy to create an electron hole pair and are efficiently absorbed.
    • Eph > EG Photons with energy much greater than the band gap are strongly absorbed. However, for photovoltaic applications, the photon energy greater than the band gap is wasted as electrons quickly thermalize back down to the conduction band edges.
    source: http://www.pveducation.org/pvcdrom/pn-junction/absorption-of-light [Broken]

    Attached Files:

    • TRA.jpg
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    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. May 23, 2016 #2

    Dr Transport

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    Gold Member

    we need more information on how the graphs were obtained, it looks like Z is either the reflectance or transmittance and X is the complement (transmittance or reflectance) and Y is the absorption, they do not indicate on the graph.
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