Recombination Analysis of Phosphorus-Doped Nanostructured Silicon Oxide Passivating Electron Contacts for Silicon Solar Cells

Abstract

We analyze the recombination properties of passivating electron selective contacts based on nanostructured silicon oxide. Our contact design is based on an interfacial buffer oxide capped with a bilayer structure of phosphorus-doped silicon oxide and silicon which is annealed at 900 °C. We investigate in detail the effects of the initial dopant concentration in the bilayer and of the anneal dwell time on dopant in-diffusion, contact formation, and interface recombination. Our investigation addresses also the hydrogenation of interface defects and the effect of indium-tin-oxide (ITO) sputtering, allowing us to separate the interplay between enhanced field-effect passivation, Auger recombination, and interface recombination. After thermal annealing, the passivating electron selective contact presented here attains a saturation current density ( J 0) of 12.4 fA cm −2 for medium doping, which improves further upon hydrogenation to J 0 = 8.1 fA cm−2. For specific contact resistances <500 mΩ cm 2, however, higher doping concentrations are required. For those doping concentrations, the saturation current density is 13.9 fA cm−2 and increases by 10% upon sputter-deposition of an ITO layer on top of the electron selective stack.