Analysis of Surface Passivation and Laser Firing via Light-Beam Induced Current Measurements

Liquid phase crystallized silicon (LPC-Si) solar cells on glass have demonstrated 14.2 % efficiency using a heterojunction interdigitated back contact cell architecture and an absorber thickness of 13 μm. However, losses are incurred in charge collection under the majority carrier contact regions even after reducing their width to 60 -120 μm. Recently, we developed a new method to first passivate these contact fingers with a-Si:H(i) and then locally laser-fire them to maintain a low contact resistance. High resolution light beam induced current measurements were used to analyze these developments. Without a-Si:H(i), an effective minority carrier diffusion length around 19 μm under the majority carrier contacts lead to only 0.13 mA cm
^-2
being collected there. With the new method, the diffusion length was improved to 36 μm and up to 113.6 μm in the best case. The reduction of passivation in the laser-fired spots was limited to a diameter of 55 μm. Over-all, charge collection increased by 0.8 mA cm
^-2
under the electron contact. Spatial mapping of charge collection creates a clear outlook to achieve 15 % efficiency even with the current material quality by reducing the laser firing spot size and implementing the new approach on cells with larger and more uniform grains.