# Can a single photovoltaic semiconductor junction ever produce a voltage much above it's own band gap?

A simple model for a photovoltaic cell is a current source with a series resistor, and a few more items. The current from the current source is some fairly constant proportionality constant of the order of one electron hole pair per incident photon (with energy above the band gap).

In reality, I think the model breaks down at high intensity - I can't think of any way that a single photodiode run in photovoltaic mode could produce for example $100~\mathrm{V}$. The spontaneous recombination - a 2nd order process - would limit the current I of the current source in the basic model. The electrons and holes would simply be stuck in the junction if the external voltage were much above the band gap.

Question: Can the output voltage of a single photovoltaic cell ever exceed the band gap my more than a tiny amount? How much? Could a single silicon junction every produce $1.5~\mathrm{V}$? $2.0 ~\mathrm{V}$?

I need more than just a screen shot of a plot, I'd like to understand the physics that governs the maximum possible DC voltage that can be produced by a standard (e.g. silicon, GaAs-like, etc) semiconductor photovoltaic cell.

• Only if reversed biased by another source, or by stacking junctions. – Jon Custer Jul 28 '16 at 16:51
• @JonCuster so for a single isolated device, is there a one-liner (or three liner) explanation why it can't produce a voltage significantly above the band gap energy of the material used for the junction? I use "significantly" so small changes due to doping and ohmic contacts don't have to be dealt with. Is it band bending due to space charge effects that's represented by the diode in the equivalent circuit? – uhoh Jul 28 '16 at 22:43
• Well, by itself, the junction built-in potential can't exceed the band gap - once the Fermi level is flat across the junction that is all she wrote - flat is flat. – Jon Custer Jul 29 '16 at 0:35
• @JonCuster or anyone: If someone can add a somewhat complete explanation and maybe a drawing of how the bands bend as the space charge effects increase at high light intensity, that would serve as an excellent answer that I could accept. Eventually I'll do it myself just to close this off, but there's a good chance someone can do a better (concise, complete, correct) job than I can. – uhoh Aug 4 '16 at 1:50