Aluminum-Based Rear-Side PVD Metallization for nPERT Silicon Solar Cells

This paper presents the results of a detailed study on Al-based physical vapor deposition metallization for the rear side of nPERT silicon solar cells. Pure Al is compared with a barrier metallization (Al-Si/Al or Ti/Al) in terms of spiking, contact formation and back-side reflection. A degradation of cell performance with pure Al rear-side metallization due to Al spiking after thermal annealing is observed. This can be avoided either by using a spiking barrier or by using a sufficiently deep doping profile. In addition, all metallization schemes have a sufficiently low specific contact resistance <;0.2 mΩ·cm² on n⁺-Si with a sheet resistance of ~75 Ω/sq. Furthermore, the widely used front-side contact metal Ti leads to a significant short-circuit current density loss of more than 0.3 mA/cm² when applied to the rear side of a silicon solar cell due to its low reflectivity of infrared wavelengths.