Hole-Collection Mechanism in Passivating Metal-Oxide Contacts on Si Solar Cells: Insights From Numerical Simulations

Silicon heterojunction solar cells enable high conversion efficiencies, thanks to their passivating contacts which consist of layered stacks of intrinsic and doped amorphous silicon. However, such contacts may reduce the photo current, when present on the illuminated side of the cell. This motivates the search for wider bandgap contacting materials, such as metal oxides. In this paper, we elucidate the precise impact of the material parameters of MoOxon device characteristics, based on numerical simulations. The simulation results allow us to propose design principles for hole-collecting induced junctions. We find that if MoOxhas a sufficiently high electron affinity (≥5.7 eV), direct band-to-band tunneling is the dominant transport mechanism; whereas if it has a lower electron affinity (xfilm in contrast to the expectation of better performance at low trap density. These traps may assist carrier transport when present near the conduction band edge of the MoOxfilm. Our simulations predict that performance optimization for the MoOxfilm has to target either 1) a high electron affinity and a moderate doping density film or, 2) if the electron affinity is lower.