Electromotive force
Solar cell current–voltage relationship

Two internal current losses I S H + I D {\displaystyle I_{SH}+I_{D}} limit the total current I {\displaystyle I} available to the external circuit. The light-induced charge separation eventually creates a forward current I S H {\displaystyle I_{SH}} through the cell's internal resistance R S H {\displaystyle R_{SH}} in the direction opposite the light-induced current I L {\displaystyle I_{L}}. In addition, the induced voltage tends to forward bias the junction, which at high enough voltages will cause a recombination current I D {\displaystyle I_{D}} 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 I S H + I D {\displaystyle I_{SH}+I_{D}} losses and consequently the maximum output current, which for a high-quality solar cell is approximately equal to the light-induced current I L {\displaystyle I_{L}}. 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:

I 0 {\displaystyle I_{0}} 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 V T = k T q {\displaystyle V_{\mathrm {T} }={\tfrac {kT}{q}}}, which is about 26 millivolts at room temperature.
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