Measurement of the Electrical Resistance of n-Type Si Microwire/p-Type Conducting Polymer Junctions for Use in Artificial Photosynthesis

Abstract

The junction between n-type silicon microwires and p-type conducting polymer PEDOT:PSS (poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)) was investigated using a soft contact method. Dopant levels within the microwires were varied during growth to give a highly-doped region for improved contact and a low-doped region for light absorption. The low-doped region of the microwires had a dopant density of 5 × 1017 cm–3 while the highly-doped region had an increased dopant density of 5 × 1018 cm–3 over ∼20 μm. Uniform, highly-doped microwires, with a dopant density of 4 × 1019 cm–3, were used as a comparison. Regions of highly-doped n-type Si microwires (ND = 5 × 1018 cm–3 and 4 × 1019 cm–3) contacted by PEDOT:PSS showed a significantly lower junction resistance compared to the low-doped (3 × 1017 cm–3) regions of the microwire. Junctions incorporating the metal catalyst used during growth were also investigated. Microwires with copper at the interface had similar current–voltage characteristics to those observed for the highly-doped microwire/conducting polymer junction; however, junctions that incorporated gold exhibited significantly lower resistances, decreasing the iR contribution of the junction by an order of magnitude with respect to the total voltage drop in the entire structure.