Characterization of flexible thin film CIGSe solar cells grown on different metallic foil substrates

Flexible Cu(In,Ga)Se2 thin films have been deposited using a three stage process on several metallic foil substrates with different barrier and back contact layers. The main difficulty associated with metallic substrates is the possible diffusion of impurities into the CIGSe absorber layer during the high temperature deposition or annealing process.The objective of this work is to study and understand the effect of substrates and the barrier/contact layer on the internal operation of the CIGS solar cells.Therefore, electrical characteristics of CIGSe thin films have been studied using current-voltage, capacitance profiling and quantum efficiency measurements. We found that the conversion efficiency depends on the choice of the substrate material and back contact layer. An efficiency of 13% on the average was achieved.The defects levels in GIGS were studied by the means of admittance spectroscopy (AS) and deep-level transient spectroscopy (DLTS) measurements, in order to understand the correlation between the origin of these defects and CIGS solar cells performances. Different defects were detected in these cells the first one observed in most of the cells strictly resemble to N1. Other defects were only present in cells with CrN combined barrier and contact layer and thus could be assigned to impurities related to the metallic substrate or back contact.