Characteristic equation of a solar cell - function of output current and voltage


The theory of solar cells explains the process by which light energy in photons is converted into electric current when the photons strike a suitable semiconductor device. The theoretical studies are of practical use because they predict the fundamental limits of a solar cell, and give guidance on the phenomena that contribute to losses and solar cell efficiency.

To understand the electronic behavior of a solar cell, it is useful to create a model which is electrically equivalent, and is based on discrete ideal electrical components whose behavior is well defined. An ideal solar cell may be modeled by a current source in parallel with a diode; in practice no solar cell is ideal, so a shunt resistance and a series resistance component are added to the model. The resulting equivalent circuit of a solar cell is shown on the left. Also shown, on the right, is the schematic representation of a solar cell for use in circuit diagrams.

From the equivalent circuit it is evident that the current produced by the solar cell is equal to that produced by the current source, minus that which flows through the diode, minus that which flows through the shunt resistor.Shown here is the characteristic equation of a solar cell, which relates solar cell parameters to the output current and voltage.

Related formulas


I output current (A)
ILphotogenerated current (A)
I0 reverse saturation current (A)
Vvoltage across the output terminals (V)
RS series resistance (ohm)
ndiode ideality factor (1 for an ideal diode) (dimensionless)
VTthe thermal voltage (V)
RSHshunt resistance (ohm)