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 asJ_0, cont = 9 × 10²\ fA/cm²on 1.5-\ p-type float-zone silicon (FZ-Si) andJ_0, cont = 2 × 10⁴\ fA/cm²on 200-\ p-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 thatAl-p⁺layer thicknessW_ 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.