In this paper, we present a method to quickly evaluate the long-term effects of copper-containing metal stack systems for silicon solar cell front–side metallization. Copper diffusion, which is detrimental for the solar cell performance, is accelerated by exposing the cell to thermal stress. In this paper, we suggest to quantify the degree of copper diffusion into the cell by the very fast Suns- VOC technique, measuring the pseudo fill factor (pFF). Using three or more different temperatures, and assuming a certain loss in pFF corresponds to a certain depth of diffusion, the effective activation energy for copper diffusion for a given system can be extracted from an Arrhenius plot of the measured data. An extrapolation into temperature regions typical for solar cell modules under outdoor conditions allows an estimation of the fill factor loss for any operation time and temperature. Compared to time- and cost-intensive methods such as transmission electron microscopy or secondary-ion mass spectrometry, this kind of investigation requires only sparse equipment and can typically be done in 1 week per stack system.

Fraunhofer ISE's concept for an advanced metallization of silicon solar cells is based on a two-step process: the deposition of a seed layer to form a mechanical and electrical contact and the subsequent thickening of this seed layer by a plating step, preferably by light-induced plating (LIP). The concept of a multi-layer metallization is used for most of the relevant high-efficiency cell types in industry. The main advantage of this concept is that each layer can be optimized individually, i.e. the seed layer to achieve an optimal electrical and mechanical contact and the plated layer in terms of high lateral conductivity and good solderability. Solar cells results with seed layers fabricated by aerosol printing, chemical Ni plating on cells with a laser-structured dielectric layer and laser-enhanced Ni plating are presented

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