IMPACT OF ALUMINIUM THICKNESS ON THE Al-Si ALLOY FORMATION OF ALUMINIUM LOCAL BACK SURFACE FIELD SILICON WAFER SOLAR CELLS

摘要

Silicon wafer solar cells with a local back surface field (“LBSF”) formed by aluminium are currentlyintensively investigated for industrial application. The non-metallised rear surface regions of this structure arepassivated by a dielectric film, whereby this dielectric film receives line or point shaped openings for contactformation, e.g. by laser ablation. An issue that is typically observed in screen-printed Al-LBSF solar cells is theformation of voids at the rear contact between the Si substrate and the Al rear contact [1], [2], especially when usingnarrow line widths or small-diameter point contacts. These voids significantly increase the series resistance of thecells, as they reduce the Si-Al contact area, and moreover reduce the surface passivation quality of the local contactsas the Al-LBSF diffusion profile is affected. In this work a reduction in the thickness of the rear Al layer is proposedto reduce the lateral diffusion of Si and therefore reduce the void formation. We report on Al-LBSF solar cells withthermally evaporated, screen-printed and sputtered Al of various thicknesses as the rear metal contact. The impact onthe void and Al p+ layer formation is studied by photoluminescence imaging and scanning electron microscopy.Finally, Al-LBSF solar cells are fabricated using various thicknesses of the rear Al metal contact.