ABSTRACT
This chapter focuses on the "classical" admittance spectroscopy (AS), and discusses the principles and possible interpretations of admittance spectra for polycrystalline solar cells. It mainly deals with the application of AS on CIGS-based thin-film solar cells. AS implies the determination of the current response to a small alternating current bias applied to a device and the deduction of the frequency and temperature dependence of the capacitance and conductance. As indicated, usually the complex admittance of a solar cell is interpreted as a parallel circuit consisting of a capacitance and a conductance. As under realistic circumstances the barrier of the main junction is much higher than the back barrier, the conductance of the main junction can be neglected. AS is certainly an interesting characterization technique for the quality of solar cells due to its technical "simplicity". However, the interpretation of admittance spectra can be ambiguous due to several underlying mechanisms which lead to similar admittance signatures.
