Andrey Raykov

• Potential-induced Degradation (PID) is one of the most severe reliability problems for the Photovoltaic industry in the recent years. As a first step towards understanding PID, in a collaboration with SCHOTT Solar, a climate model was developed - both to map and quantify the dependence of the effect on environmental factors like temperature and relative humidity, and to find a method to screen materials for susceptibility to PID. Such investigations allow for the lifespan of a standard PV module to be predicted depending on the environmental conditions, installation properties and the building components of the module. Additionally, the thermal regeneration under variety of conditions was studied, both to mitigate the effect and collect more information for model building. Furthermore, the leakage current behavior and its correlation to PID was studied. As an alternative, a two-step lifetime warranty test for PID was designed and developed. The second part of this thesis, together with SolarWorld Innovations, focused on investigating the root cause of PID. Three root-cause hypotheses were developed and tested – the Li Hypothesis, the Inversion Layer Hypothesis and the other hypothesis involving the decoration of stacking faults with sodium. These theses were critically evaluated, partially refuted and eventually extended by the proposition that those stacking faults (and other crystal defects) have process-induced nature. One critical approach to limit PID on cell level was studied in further depth – the emitter oxidation. During the course of this work, PID was observed to be a rather polyvalent defect mechanism – it was made obvious that more defect mechanisms contribute to PID. The process-induced crystal defects during high-temperature processing (as well as contaminants in the silicon) was identified as one of the most important mechanisms. It could explain a number of the complex phenomena and non-uniformities on cells and module level related to PID.