A unique feature of the QuickSun software is the Irradiance Decay Cell Analysis Method, IDCAM. It solves the 2-diode model of a silicon solar cell during the single I/V curve measurement.
The 2-diode model is a well known and physically reliable description for crystalline silicon cells consisting of five components which are i) ideal diode, ii) recombination diode, iii) shunt resistance, iv) series resistance and v) current source representing the irradiance induced current. This equivalent circuit with its mathematical equation is depicted in the QuickSun screenshot picture 1.
In order to solve the 2-diode equation, the standard I/V curve measurement is followed by the measurement of open circuit voltage when irradiance continues to fall during the tail of the flash pulse, see an example picture 2. Since there is no current flowing through the series resistance, the 2-diode equation simplifies essentially. The diodes and the shunt resistance can be extracted from each other due to their different voltage dependencies. At high voltages the ideal diode behavior dominates, at medium voltages depletion layer recombination current can be distinguished and at low voltages only the effect of the shunt resistance is observed. A simple least square fitting method can be applied. After this the only remaining unknown component, series resistance, is evaluated by fitting the initially measured voltage, current and irradiance signals.
After the five parameters have been solved, the 2-diode equation can be used to draw the corresponding I/V curve. In the picture 3, a sample screen shot of the QuickSun software is shown. The I/V curve obtained from the IDCAM analysis is shown on the top right part of the screen shot with blue, and it is overlapping the actual measured I/V curve (red) almost perfectly. The differences between the curves can give additional information on the finger and emitter layer conductivity.
Although the analysis and the equation is designed to be used on single cells only, the method has been proven to be effective in module analysis also. Relevant articles concerning IDCAM can be found in the Articles section.