Ni/Cu electroplating, a worthwhile alternative to use instead of Ag screen-printed front side metallization of conventional solar cells

Abstract

For commercial purposes, it is necessary to manufacture high-efficiency and low-cost solar cells using simple processes. The front contact formation is one of the most critical steps in solar cell processing. Although silver paste screen-printed solar cells are the most widespread on the photovoltaic market, their efficiency is strongly limited as a result of shading and resistive losses, or more precisely the high contact resistance. Cu metallization for crystalline Si solar cells has attracted much attention as an alternative to the screen-printing technology. The low-cost Ni/Cu metal contact is regarded as the next generation of metallization processes to still improve the efficiency with a low specific contact resistance; it is formed using low-cost electroless plating and electroplating. A diffusion barrier should be placed between Cu and Si, to prevent Cu diffusion. Ni is shown to be an adequate barrier to Cu diffusion. For these reasons, geometry optimization of metal contacts of the front face, deposited by commercial processes, is investigated in this paper, in order to improve the spectral response of conventional multicrystalline mc-Si silicon solar cells. Their efficiency variation is analyzed as a function of changes in cell parameters (finger separation distance, height and width of finger, sheet resistance emitter...) using simulation programs in MATLAB, using contours to represent the efficiency evolution in terms of two variables. Efficiency gain of more than 0.7% has been achieved in this study. The simulation results were then compared with experimental data in order to be validated.