Firing-Stable PECVD SiO_xN_y/n-Poly-Si Surface Passivation for Silicon Solar Cells

Passivating contacts based on SiOx/poly-Si exhibit excellent contact and surface passivation properties enabling very high solar cell conversion efficiencies. In this paper, we investigate and optimize the plasma-enhanced chemical vapor deposition (PECVD) of SiOxNy/n-a-Si stacks, their subsequent annealing to SiOxNy/n-poly-Si stacks followed by PECVD SiNx deposition and firing. We eliminate blistering of the poly-Si layer by enabling a controlled hydrogen out-diffusion during the annealing step. Whereas the J0 of thermal SiOx/n-poly-Si stacks degrade after firing, PECVD SiOxNy/n-poly-Si stacks exhibit excellent firing stability enabling J0 values down to 1.3 fA/cm2 after firing which corresponds to an outstanding implied VOC of 744 mV. The application of different hydrogenation processes to the thermal SiOx/n-poly-Si and PECVD SiOxNy/n-poly-Si stacks reveals that both stacks achieve excellent passivation properties with J0 = 1.5 fA/cm2 after maximum hydrogenation. However, only the PECVD SiOxNy/n-poly-Si stack maintains this excellent surface passivation after firing possibly due to a superior capability to retain the hydrogen at the c-Si/SiOxNy interface during firing and thus demonstrates the potential as a future manufacturing process sequence.