Suppose there is a solar cell with light of a single wavelength shining on it (through air) and that this wavelength is optimal for the cell, meaning that it is converted to electricity with the highest efficiency.

What would happen if that cell was placed in a medium other than air? Would the wavelength of the light be altered in such a way that the output/efficiency of the cell would be different (ignoring how the medium impacts the cell itself)?

  • 1
    $\begingroup$ The wavelength internal to the cell remains the same, so no change there. However, if there is an anti-reflection coating on the cell you probably just messed up the efficiency of getting that wavelength into the cell... $\endgroup$
    – Jon Custer
    Commented Jan 12, 2015 at 22:49
  • $\begingroup$ Is there any way to change the speed of propagation within the cell (e.g. if the entire cell was suspended in some inert, transparent compound)? Or is air somehow essential to the way the cell converts the energy? Thanks again Jon! $\endgroup$
    – Eric Czech
    Commented Jan 12, 2015 at 23:02
  • $\begingroup$ No. Propagation and absorption in the cell depends only on the properties of the cell. Getting the photons into the cell depends on the external medium through the reflection coefficient of the boundary (and angular variation of the reflection coefficient). The air is not essential at all - it just is the medium transporting photons to the cell. Many cells have an index matching layer on them to increase transmission into the semiconductor, so the photons aren't even entering the cell proper from air. $\endgroup$
    – Jon Custer
    Commented Jan 12, 2015 at 23:20
  • $\begingroup$ @EricCzech This might not be what you were wondering about, but some of the light will be shifted in wavelength due to vibrational Raman scattering. It would require a thick layer of water to get significant Raman scattering though, and some scattered light not reaching the solar cell at all would probably have a larger effect on the efficiency than the wavelength shifts. $\endgroup$
    – jkej
    Commented Jan 13, 2015 at 17:24

1 Answer 1

  1. The spectrum will be filtered

This causes a drop in efficiency. For single junction cells, which are very tolerant to changes in spectrum, the drop will be much less than for multi junction solar cells which are designed for particular spectral conditions.

  1. Leakage current

The IV characteristic will change because the surface resistance will decrease causing a leak current. This will also reduce efficient.

  1. Reflection at the surface will change.

Reflection occurs at the interface between materials of different refractive index. Semiconductor have a high index, say around 3.5, so the reflection is high. For these reasons solar cells have surface antireflection treatment which tries to place a materials of intermediate index between the surface and air (#1). If you place this in water you will skew this behaviour away from the design specification.

(#1) the details here are quite fascinating, I slightly over simplified this point.


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