Quick Determination of Copper-Metallization Long-Term Impact on Silicon Solar Cells

Abstract

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- 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.