Molybdenum contamination of silicon can have serious detrimental consequences for the efficiency of solar cells, raising durability concerns for novel solar cell designs that utilize $\mathrm{Mo}{\mathrm{O}}_3$ in contact with Si. Density functional theory simulations of Mo defects in Si revealed that Mo is preferentially accommodated in tetrahedrally coordinated interstitial sites and that the contamination may reach a sufficiently high concentration to cause a 20% relative solar cell efficiency degradation if processing steps are performed between 950 and 1300 K. The formation energy of the most energetically favored Mo defect in Si has a minimum value of 1.58 eV at the valence band maximum and a maximum of 2.10 eV at higher Fermi levels, indicating that higher Mo defect concentrations may occur in $p$-type Si than intrinsic or $n$-type Si. The diffusion processes for Mo in Si were investigated, and it was identified that interstitial diffusion dominates over a vacancy-mediated mechanism under all equilibrium conditions. Migration barriers were calculated to be 2.29 eV for charge neutral and 2.03 eV for charge +1 defects, occurring under $n$-type and $p$-type doping, respectively, indicating that Mo diffusion is faster in $p$-type Si, and hence potentially more effectively gettered than it would be in $n$-type Si.

• Received 25 September 2019
• Accepted 14 January 2020

DOI:https://doi.org/10.1103/PhysRevMaterials.4.025403