The IV curve of a solar cell is the superposition of the IV curve of the solar cell diode in the dark with the light-generated current. The light has the effect of shifting the IV curve down into the fourth quadrant where power can be extracted from the diode. Illuminating a cell adds to the normal "dark" currents in the diode so that the diode law becomes:
where IL = light generated current.
The equation for the IV curve in the first quadrant is:
The -1 term in the above equation can usually be neglected. The exponential term is usually >> 1 except for voltages below 100 mV. Further, at low voltages the light generated current IL dominates the I0 (...) term so the -1 term is not needed under illumination.
Several important parameters which are used to characterise solar cells are discussed in the following pages. The short-circuit current (ISC), the open-circuit voltage (VOC), the fill factor (FF) and the efficiency are all parameters determined from the IV curve.
- 1. , “Application of the superposition principle to solar-cell analysis”, IEEE Transactions on Electron Devices, vol. 26, pp. 165–171, 1979.