Imaging characterization techniques applied to Cu(In,Ga)Se2 solar cells

The authors present examples of imaging characterization on Cu(In,Ga)Se-2 (CIGS) solar cell devices. These imaging techniques include photoluminescence imaging, electroluminescence imaging, illuminated lock-in thermography, and forward- and reverse-bias dark lock-in thermographies. Images were collected on CIGS devices deposited at the National Renewable Energy Laboratory with intentional spatial inhomogeneities of the material parameters. Photoluminescence imaging shows brightness variations, which correlate to the device open-circuit voltage. Photoluminescence and electroluminescence imaging on CIGS solar cells show dark spots that correspond to bright spots on images from illuminated and forward-bias lock-in thermography. These image-detected defect areas are weak diodes that conduct current under solar cell operating conditions. Shunt defects are imaged using reverse-bias lock-in thermography. The authors show how imaging can be used to detect structural defects detrimental to solar cell performance. The images provide defect locations that are analyzed in more detail by scanning electron microscopy techniques using top view and cross section imaging. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3358303]