Influence of the Al-Si Alloy Formation in narrow dielectric barrier openings on the specific contact resistance

in order to further improve the efficiency of multicrystalline solar cells, both a dielectric passivation and local contact formation at the rear are important design contributions. The dielectric passivation presents many advantages compared to the standard fully covered Al back contact. Our work is centred in the analysis of the contact formation between Al and Si for the passivated emitter and rear cell device structure, PERC. We give an experimental explanation for the observed dependence of the contact resistivity of Al fingers on the Si-contact area. Our observation is based on the analysis of the geometry of the Al-Si alloy formation below the contacts, giving important conclusions for PERC solar cells. Scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS/EDX) supports the analysis of the Al-Si alloy geometry, giving an understanding of its formation, and effect on the contact resistivity.