Hydrogen Stability and Bonding in SiNx and Al2O3 Dielectric Stacks on Poly-Si/SiOx Passivating Contacts

Polycrystalline Si on SiO_x passivating contacts enables some of the highest efficiency single-junction Si photovoltaic devices, but the high-temperature firing process needed for industrial metallization can significantly reduce passivation. We show that after firing, the implied open-circuit voltage, iV_oc, for the Al₂O₃/SiN_x/poly-Si/SiO_x/c-Si stack is 20-30 mV higher than the SiNx/Al₂O₃/poly-Si/SiO_x/c-Si stack and therefore provides better passivation of the SiO_x/c-Si interface. Using effusion measurements and Fourier transform infrared spectroscopy, we demonstrate that more than twice as much hydrogen is retained in the dielectric up to the peak firing temperature of ~800 degrees C for Al₂O₃-capped structures. If the Al₂O₃ layer is not present in the stack, after firing, the iVoc is lower by 50-100 mV compared to Al₂O₃/SiN_x or SiN_x/Al₂O₃ stacks. These studies will inform future work on the role of dielectrics in aiding the passivation of poly-Si/SiO_x passivating contacts.