Surface Functionalization of Silicon Microwires for Use in Artificial Photosynthetic Devices

Abstract

Integrated photoelectrochemical water splitting with sunlight is one possible solution to growing global energy needs. Integration of catalysts, photoabsorbers and a membrane require low barriers to charge dissipation if a free standing device structure is to be achieved. The n-type/PEDOT:PSS junction has be identified as the major resistive component and constitutes a large barrier to charge dissipation. In this thesis, the modification of the interface between n-type Si/PEDOT:PSS was achieved by growing a highly – doped region at the contact between the wire and the membrane to reduce voltage loss at the junction from 300 mV to 130 mV. In addition, modification of the surface using a thiophene moiety is observed to decrease the voltage loss from 300 mV to 30 mV. Formation of an insulating silicon oxide on the methyl functionalized surface of the microwires identified a need for characterization of planar silicon samples representative of the sides of the microwires. Si (110), (211) and (111) crystal faces were functionalized with a methyl group and showed different resistance to oxidation. The Si (111) surface was the most resistant while the Si (211) surface was observed to be the least resistant to ambient oxidation.