Barriers for current transport in CIGS structures

A potential barrier impeding current flow in the forward direction is observed in some CIGS devices especially at low temperature. In this paper possible origin and location of this barrier is discussed. We have taken into account: a front contact barrier in the window layer, front contact barrier due to the p+ layer, and back contact barrier at CIGS/Mo interface. The discussion is based on current-voltage, capacitance-voltage and admittance spectroscopy data measured for CIGS cells with CdS and In₂S₃ buffer layers and with Mo and Pt back electrode. Accumulated evidences point towards a front electrode as a source of the barrier in the CdS-buffered cells. We show that the height of this barrier is influenced not only by properties of the buffer but also by sodium supply.