I was wondering how different energy photons interact with the electrons in a semiconductor in a PV cell. If the photon has less energy than the band gap, then the photon passes through and does not interact with the semiconductor, right? Does it just keep traveling until it hits a material beneath the PV cell that can absorb it? If the photon has more energy than the band gap, then where does the excess energy go after the electron has been promoted to the conduction band? Is this heat energy?


1 Answer 1


If the photon has less energy than the bandgap, it will not be absorbed and the material is theoretically transparent to this wavelength as you can see here:


If the energy is higher than the bandgap energy (a little) it can still be absorbed as seen here


The absorption, although, is not fully efficient and the excess of energy will be lost, as you said, in heat, during the process in which it is transformed in electrical energy.

  • $\begingroup$ I'm confused by the 'not fully efficient' part - the photon is absorbed. An electron-hole pair is created. Yes, the electron will rapidly thermalize down to the band edge. Furthermore, the conduction band is often several eV wide, so once you start absorbing you keep absorbing for some time. $\endgroup$
    – Jon Custer
    Jul 24, 2017 at 0:38
  • $\begingroup$ Do you have any other photovoltaic/solar cell links like those that go into extreme detail? I already have solarcellcentral.com $\endgroup$ Jul 24, 2017 at 1:36

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