Contact Formation and Recombination at Screen-Printed Local Aluminum-Alloyed Silicon Solar Cell Base Contacts

We study recombination properties and the formation of base contacts, which are realized by local laser ablation of a dielectric stack and the subsequent full-area screen printing of an Al paste. Based on charge-carrier lifetime measurements using the camera-based calibration-free dynamic infrared lifetime mapping technique, we determine contact reverse saturation current densities as low as J_{0, cont} = 9 X10² fA/cm² on 1.5-Ωcmp-type float-zone silicon (FZ-Si) and J_{0, cont} = 2X10⁴ fA/cm² on 200- Ωcmp-type FZ-Si. Scanning electron microscopy images reveal that the thickness of the highly Al-doped (Al-p⁺) layer considerably depends on the contact size and the contact layout (e.g., point or line contacts). Based on this finding, we show that Al-p⁺ layer thickness W_Al-p+ significantly affects the contact recombination. As a result, we show which local contact geometry is most appropriate for the lowest contact recombination employing local Al-alloyed contacts.