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.

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At Fraunhofer ISE the fabrication of high-efficiency solar cells was extended from a laboratory scale to a small pilot-line production. Primarily, the fabricated cells are used in small high-efficiency modules integrated in prototypes of solar-powered portable electronic devices such as cellular phones, handheld computers etc. Compared to other applications of high-efficiency cells such as solar cars and planes, the illumination densities found in these mainly indoor applications are significantly below 1 sun. Thus, special care was taken to keep the cell efficiency level high even at very low illumination levels. For this reason, particularly the cell border was analyzed and optimized carefully. The excellent cell characteristics achieved at low illumination densities increase the benefit of a solar power supply for such devices by an order of magnitude if compared to standard solar cells

This study deals with some specific characteristics that the light-induced plating (LIP) process, which is used for the metallisation of solar cells, exhibits compared to classical electroplating processes. We contribute to the general understanding of LIP (multiple electrodes, influence of light) with some basic experiments and propose a simplified equivalent circuit scheme. We also address the challenge of process control through potential and current without external connection of the working electrode (front side grid). In this article, we show a possibility to determine the absolute potential of the front side grid for relevant process parameters. Furthermore, we present a method that allows the measurement of the mean current density at the front side grid during the process, which has a great influence on the plating result

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