An effective medium approach for modeling polycrystalline silicon thin film solar cells

A simple and fast 1D effective medium simulation model for polycrystalline silicon thin film solar cells was defined, by using the device simulator AFORS-HET. The model was calibrated with current-voltage measurements of solar cells under illumination and in t he dark. The experimentally determined variation of the solar cell characteristics with varying absorber doping and absorber thickness can be reproduced by the model. Through inverse modeling, the effective defect density in the absorber layer was determined and it was shown that the open circuit voltage VOC of the cell is limited by defects localized in the bulk of the absorber layer. Using the calibrated simulation model for sensitivity analyses, different optimization strategies for this type of solar cells have been assessed. Firstly, the optimum absorber thickness as a function of absorber doping and defect densities has been determined and secondly, the VOC-increase when using a layer of hydrogenated amorphous silicon (a-Si:H) to form a heterojunction back surface field has been simulated as a function of the absorber defect density.