Admittance and impedance spectroscopy on Cu(In,Ga)Se2 solar cells

Abstract

The present work reports some experimental results on the electrical properties of high efficiency ZnO/CdS/Cu(In,Ga)Se2 heterojunction solar cells. Admittance spectroscopy has been employed for characterisation of the bulk and interface levels in the absorber Cu(In,Ga)Se2 layer. The temperature dependent capacitance-frequency analysis indicated an emission from a shallow acceptor like defect level with an activation energy of about 75 meV. Information on the equivalent circuit model of the devices has been provided by the analysis of impedance measurements. The impedance data are presented in the Nyquist plot at several dc bias voltages at 300 K. The equivalent circuit model consisting of a parallel resistor and capacitor in series with a resistor is found to give a good fit to the experimental data.