Interdigitated Metallisation Pattern Design based on Lumped Series Resistance Calculations

Abstract

An interdigitated metallisation scheme was developed and optimised for polycrystalline silicon thin-film solar cells on glass. In the investigated metallisation approach, polycrystalline silicon is partially and selectively removed from the glass substrate in order to contact the emitter of the cell, which is located at the glass-side surface of the solar cell. In this metallisation approach, the design of the metal pattern is of key importance. On the one hand, if the number of fingers on the glass side is too small, a significant part of the photogenerated charge carriers will be lost due to recombination. On the other hand, if active material is removed, the area covered with absorbing material decreases and the number of absorbed photons is reduced. To optimise the metal pattern, a model based on the lumped series resistance of the metal pattern is used to provide analytical solutions for the different resistive losses. The impact from the size of the glass-side contacting area and the number of glass-side fingers on the electrical properties of the polycrystalline silicon thin-film solar cells is investigated based on this model. It is found that for a poly-Si thin-film solar cell with current density of 19 mA/cm2 and pseudo fill factor of 74%, a metal pattern with 500 μm pitch and 15 μm emitter finger width results in the minimum power loss due to metallisation.