Comparison of D.C. and A.C. electro-analytical methods for measuring diode ideality factors and series resistances of silicon solar cells

The diode ideality factor (m) and the series resistance (Rs) of a Si solar cell represent two critical performance-indicator parameters of the device. Since both m and Rs are functions of voltage (V) and temperature (T), simultaneous electrical measurements of these parameters under variable conditions of V and T can often be difficult with traditional direct current (D.C.) techniques. Using the electro-analytical method of linear sweep voltammetry (LSV) and a commonly available Si solar cell, we explore these specific confines of such D.C. measurements. The results are compared with those obtained from a parallel set of alternating current (A.C.) measurements using impedance spectroscopy (IS). LSV provides the main D.C. parameters (open circuit voltage, short circuit current, fill factor, and efficiency) of the cell, but is limited in terms of independently measuring m and Rs beyond strong forward biased conditions. The IS approach is free of the latter experimental constraints, and at the same time can provide several other important electrical parameters of the solar cell. Specifically, IS detects the presence of a low-high (p–p+) junction at the back surface of the cell, and serves as an efficient probe of certain electrical characteristics of this junction.