Process Control and Defect Analysis for Crystalline Silicon Thin Films for Photovoltaic Applications by the Means of Electrical and Spectroscopic Microcharacterization Tools

This paper demonstrates the usefulness of optical microcharacterization for process control and defect analysis for epitaxial grown crystalline silicon thin films (cSiTF). Using a confocal laser scanning microscope, we gradually analyze material and electrical properties of epitaxial grown cSiTFs and interface quality between cSiTF and substrate on the microscopic scale. With micro-Raman spectroscopy, the interface quality and the doping density within the epitaxial layers are evaluated. Microphotoluminescence spectroscopy investigations reveal the highly recombinative character of stacking faults decorated with strongly deformed silicon fractions that are frequently formed during epitaxial growth at low temperatures. The microlight beam-induced current delivers detailed information about local inhomogeneities of the charge collection. Finally, these methods are applied to fully processed solar cells with an epitaxial absorber. A globally observed cell voltage drop is linked to parasitic metal deposition on highly recombination active pyramidal stacking faults in the epitaxially grown cSiTF layers. By means of microreverse-biased electroluminescence, it is shown that this parasitic metal deposition on stacking faults causes local prebreakdowns.