Scribing Defects in CIGS Modules

Abstract

For achieving a monolithic series connection of cells in a Cu(In,Ga)Se2 thin film module, in most cases a combination of laser scribing and mechanical scribing steps is used. Interruptions in these scribing processes can severely deteriorate the module efficiency. In this work we investigate the use of spatially resolved electroluminescence (EL) images for identifying and characterizing such scribing defects. Electroluminescence imaging allows determining local junction-voltage differences within a solar cell, and thus is sensitive to scribing defects. Furthermore, EL imaging is fast allowing its use as an inline metrology tool. In this work we use a simulation tool based on the network simulation method to simulate the local junction voltage variations within cells in a module. Using this simulation tool we determine EL image signatures of various types of scribing defects, which can be used to identify real scribing defects. We investigate defective scribing lines through the molybdenum back contact, the CIGS absorber and the transparent conductive oxide. In order to verify our simulations we experimentally implement scribing interruptions of varying lengths and record EL images of the defects. We find the simulations and experiments are in good agreement.