On the Nature of the One-Diode Solar Cell Model Parameters

The one-diode model is probably the most common equivalent electrical circuit of a real crystalline solar cell. Extensive research has focused on extracting model parameters from measurements performed in standard test conditions (STC), aiming to replicate the current-voltage characteristics (I-V). This study started from finding that, for the same solar cell, different scientific reports yield significantly different sets of parameters, all allowing for highly accurate replication of the measured I-V characteristics. This observation raises a big question: What is the true physical set of parameters? The present study attempts to address this question. For this purpose, a numerical experiment was conducted. The results show that there is an infinity of distinct sets of parameters that can replicate the I-V characteristics at STC via the one-diode model equation. The diode saturation current IS and the diode ideality factor compensate each other to preserve the open-circuit voltage VOC, always an input data point. Some possible approaches (e.g., the link between VOC and IS) that can lead to the physical set of parameters are discussed, highlighting their strengths and weaknesses. There is enough room for future research on finding a universal approach able to guarantee the accurate extraction of the one-diode model physical parameters.