Defect diagnostics for cadmium telluride thin film solar cells
New methods for high-resolution electro-optical, electron and ion beam based tools for defect diagnostics are of major importance for quality control and process monitoring in industrial scale thin film solar cell production. In the present work electro-optical methods like Lock-in Thermography (LIT) are applied for the detection of defects, e.g. shunts and recombination active regions, in PV thin film systems. For the "in situ"- defect localization in scanning electron microscopy (SEM), electron beam induced current (EBIC) measurements are an appropriate tool, which allows the application of SEM methods for elemental and material analysis on nm scale. Furthermore, examples are presented which demonstrate target preparation using focused ion beam technology (FIB) for root cause analysis within the multilayer stack. For microscopic defects at thin film cells and at laser scribed interconnects the local electric properties have been measured using four point probing with micro tips. Advanced preparation methods have been applied for the electrical insulation and contacting on a micro-mscale. In particular, the use of ion erosion has been found to be highly useful for the well defined insulation of thin film layers. Thus, the local resistance of individual shunts as well as local I-V-characteristics has been determined.