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In the textbook : Electric Power Principles, in Chapter 1

on the working of a pv cell :

The source current Is is the result of absorption of photons in sunlight that cause separation of valence electrons from their atoms. The resulting hole/electron pairs fall across the high field gradients present at the diode junction. Because any voltage resulting from this current tends to forward bias the actual junction, the voltage available is limited

I don't understand the train of thought leading to a limited voltage, and I'd appreaciate a better explaination or a reading recomendation.

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  • $\begingroup$ electronics stack exchange is probably better for this $\endgroup$
    – agentp
    Feb 18, 2018 at 3:04
  • $\begingroup$ This is a question about the machanism of P-N Diodes, not PV Cells $\endgroup$
    – Jonathan R Swift
    May 21, 2018 at 14:08

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The simplest explanation I can give is that a forward biased diode will start to transmit a high level of current with only a small increase in voltage, once a certain threshold is reached. This means that if you increase the rate at which electrons are generated with more sunlight, then instead of the voltage increasing in line with this, the current will go up instead. There are numerous resources explaining the mechanisms behind this elsewhere on Electronics SE, and the wider internet.

If you would like a higher voltage for a particular project, you can simply connect multiple solar cells in series.

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A photovoltaic device is a device that generate voltage when exposed to light. Example of photovoltaic device is a solar cell.The photovoltaic effect was discovered by Alexander-Edmond Becquerel in 1839, in a junction formed between an electrode (platinum) and an electrolyte (silver chloride). It uses n-type semiconductor substrate. A trivalent impurity is diffused on its top surface such that a thin p-type layer is formed. Metallic contacts are formed on both the layers for external circuit connections. Top surface is coated with antireflecting material to increase absorption of light energy. Finally it is covered with thin protecting glass. While junction is forming, depletion layer and potential barrier builds up because of crossing of majority carriers across the junction. When photon of energy greater than band gap(>Eg) are incident on the cell, the photons are absorbed and electron-hole pairs are generated. The barrier potential segregates them and pushes electrons to n-side and holes in p-side. This displacement of charges sets up a p.d(photo voltages) across two regions, with p-side as +ve and n-side as -ve electrode. If external load Rl is connected, current flows through it and we get electrical energy. Typically a solar cell can generate photovoltage from 0.5V to 1.2V. Solar cells are connected in series and parallel to increase voltage and current capacity. Such combination of solar cells is called photovoltaic array.Photovoltaic cells are used in infrared detectors, light intensity calculators, solar fans, solar heater and solar panels etc.A solar panel consists of hundreds or thousands of photovoltaic cells mounted together in the form of a huge cell module.

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  • $\begingroup$ That’s a great explanation but it doesn’t answer why the voltage is limited to that value, or am I missing something $\endgroup$
    – sarah
    Feb 24, 2018 at 13:49
  • $\begingroup$ In specific my question is on “ because the voltage resulted from this current tends to forward bias the actual junction “ $\endgroup$
    – sarah
    Feb 24, 2018 at 13:51

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