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This paper reports on a methodology to achieve low-cost high-efficiency screen-printed low-to-medium concentrator Si cells and validates it by fabricating some of the highest efficiency metal paste printed cells with a simple cell design. The model shows that the highest achievable efficiency at any given concentration is a function of metal paste, contact parameters, number of fingers, and finger length due to the tradeoff between resistive and shadow losses. Consistent with the model calculations, first, 52 mm × 27 mm ~19% cells were fabricated at ~5X (suns) with a Dupont 16 A paste and ~110 μm wide 32 lines. Then, with improved 50 μm wide direct extrusion printed fingers, >20% efficient cells were achieved in the concentration range of 3-16X, along with a roadmap to ~21% efficient cells. This approach provides excellent guidelines to design grid pattern and selecting cell dimensions to achieve maximum efficiency at the desired concentration from a given printing technology and cell structure.
Date of Publication: July 2013