ON THE INTERPRETATION OF ADMITTANCE AND IV(T) MEASUREMENTS OF CIGS THIN FILM SOLAR CELLS

摘要

Cu(In,Ga)Se2 (CIGS) is the most promising thin film technology with cell efficiencies exceeding 21% on a laboratory scale. Nevertheless, quite some properties of these devices are not well understood. In this contribution admittance spectroscopy and current-voltage (temperature dependent) (IV(T)) measurements are compared and interpreted with respect to properties of the CIGS-Mo back contact. One important point of discussions is the interpretation of the N1 -step observed in admittance spectroscopy measurements for CIGS thin-film solar cells. In some theories the N1-step is related to a Schottky barrier at the back contact. From admittance spectroscopy it is possible to deduce the associated barrier height. From temperature dependent current-voltage-measurements (IV(T)) it is also possible to deduce the existence of a Schottky barrier and determine the barrier height by using the open circuit voltage (V_(oc)) over temperature characteristic. However, the values of this barrier as obtained experimentally from these two methods differ significantly. Looking more closely at the measurement conditions of admittance spectroscopy it is obvious that the small signal properties are measured. Thus, with respect to IV(T) measurements also the properties in the dark at a low positive bias of round about 0.1 to 0.2 (corresponding to the conditions during admittance spectroscopy) showed a good agreement. Based on these findings a possible explanation of the derivation is a dominant shunt resistance in the low bias regain where the admittance is measured.