Analysis of fitted Suns-Voc curves using two-diode model

The light intensity vs open circuit voltage (Suns-V_oc) measurement technique has been extensively used in characterising nonmetallised thin film silicon solar cells. Unlike the short circuit current vs open circuit voltage (Isc-V_oc) measurement, Suns-V_oc presents a great advantage by operating in a simple quasi-steady-state. Because the equipment used in Suns-V_oc is far less complex than the equipment used in the normal l_sc-V_oc measurement, it is a very practical method to promptly determine the open circuit voltage (V_oc) of solar cells, especially during the initial processing steps. Using this technique, the one-sun open circuit voltage data and other relevant parameters were extracted from a Suns-V_oc spreadsheet while a fitted Suns-V_oc curve was used as a standard graphical reference for analysing the Suns-V_oc results. As Suns-V_oc results were recorded after each process, the properties of a solar cell such as shunt and two-diode model behaviour could be tracked down quickly when required. By integrating all the results from each measurement done, necessary interpretation of solar cell´s performance could be made. A distinct advantage is that the measurement can be done at most fabrication sequence even before a solar cell is metallised. In this paper, fitted Suns-V_oc curves are analysed to extract the diode properties of silicon solar cells.