Editing Electromotive force (section)

==== Solar cell current–voltage relationship ====
Two internal current losses <math>I_{SH} + I_D</math> limit the total current <math>I</math> available to the external circuit. The light-induced charge separation eventually creates a forward current <math> I_{SH}</math> through the cell's internal resistance <math>R_{SH}</math> in the direction opposite the light-induced current <math>I_L</math>. In addition, the induced voltage tends to [[p-n junction#Forward bias|forward bias]] the junction, which at high enough voltages will cause a recombination current <math> I_{D}</math> in the diode opposite the light-induced current.

When the output is short-circuited, the output voltage is zeroed, and so the voltage across the diode is smallest. Thus, short-circuiting results in the smallest <math>I_{SH} + I_D</math> losses and consequently the maximum output current, which for a high-quality solar cell is approximately equal to the light-induced current <math> I_{L}</math>.<ref name="Lorenzo">{{cite book
 |title=Solar Electricity: Engineering of photovoltaic systems
 |editor=Eduardo Lorenzo
 |first= Gerardo L.|last=Araújo
 |chapter-url=https://books.google.com/books?id=lYc53xZyxZQC&pg=PA74
 |chapter=§2.5.1 Short-circuit current and open-circuit voltage
 |isbn=978-84-86505-55-4
 |year=1994
 |page=74
 |publisher=Progenza for Universidad Politechnica Madrid
 }}</ref> Approximately this same current is obtained for forward voltages up to the point where the diode conduction becomes significant.

The current delivered by the illuminated diode to the external circuit can be simplified (based on certain assumptions) to:

:<math>I = I_L -I_0 \left( e^{\frac{V}{m\ V_\mathrm{T}}} - 1 \right) \ . </math>

<math>I_0</math> is the [[reverse saturation current]]. Two parameters that depend on the solar cell construction and to some degree upon the voltage itself are the [[ideality factor]] ''m'' and the [[thermal voltage]] <math>V_\mathrm{T} = \tfrac{k T}{q} </math>, which is about 26 millivolts at [[room temperature]].<ref name= Lorenzo/>