Kamal Katkhouda

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.

Quick Determination of Specific Contact Resistance of Metal–Semiconductor Point Contacts on Highly Doped Silicon

This paper presents a characterization method to determine specific contact resistance of metal-semiconductor point contacts on a highly doped silicon. The method uses a symmetrically doped silicon wafer with full area contact on the front side and point contacts on the rear side. The specific contact resistance of point contacts is determined by measuring the resistance of the sample for various contact spacing values. The extraction of the specific contact resistance from the measured sample resistance is done by using a simplified analytical model, which is verified with time-intensive numerical 3-D device simulations. Furthermore, the specific contact resistance range that is detectible with this approach is investigated. In addition, the use of this method is tested for point contacts opened with laser ablation and metalized with physical vapor-deposited aluminum on two different phosphorous doping profiles. Finally, the results obtained by this method are verified with cell results of nPERT solar cells. The presented method can be applied to develop and control contact opening, metalization, and contact formation annealing processes for silicon solar cells with point contacts on highly doped regions, especially for the development in an industrial environment.