Electrical characterization of microwire-polymer assemblies for solar water splitting applications

• Main Author: Yahyaie, Iman
• Other Authors: Oliver, Derek (Electrical & Computer Engineering) Thomson, Douglas (Electrical & Computer Engineering)
• Published: American Chemical Society 2012
• Subjects: Solar water-splitting; Artificial photosynthesis; silicon microwire; conducting polymers; organic semiconductor
• Online Access: http://hdl.handle.net/1993/9225

The increasing demand for energy and the pressure to reduce reliance on fossil fuels encourages the development of devices to harness clean and renewable energy. Solar energy is a large enough source to fulfill these demands, however, in order to overcome its daily and seasonal variability, it has been proposed that sunlight be harvested and stored in the form of chemical fuels. One potential approach is the photosynthetic splitting of water to store solar energy in the simplest chemical bond, H–H, using a device that includes: semiconducting microwire arrays as light harvesting components, redox catalysts, and a membrane barrier for separating the products of water redox reactions.. However, the harvested solar energy can be lost across the system and it is critical to characterize the electrical properties of each component within the system to quantify how much of this energy will ultimately be coupled to the water splitting reactions. The aim of this research is to develop approaches for characterization of a proposed system of this kind, incorporating individual semiconductor microwires as photoelectrodes (with no redox catalysts) embedded into a candidate conducting polymer membrane to form a single functional unit. Semiconductor microwires were isolated and using a novel contact formation approach with tungsten probes in a standard probe station, and their current versus voltage properties were characterized. This approach is of particular interest when ii considering the limitations of conventional contact formation approaches (e.g. thermal evaporation of contact metals), arising from the small dimensions of the microwires and also the incompatibility of these techniques with many microwire/polymer structures due to the unwanted interactions between polymers, photoresists, etchants and the high temperature lithographic processes. The electrical properties of different microwires and also the junctions between microwires and two candidate polymers were studied. Specifically, the combination of methyl-terminated silicon microwires and PEDOT:PSS:Nafion demonstrated promising behavior, with a total DC resistance of approximately 720 kΩ (i.e. losses < 16 mV at maximum available photocurrent), making it a suitable candidate for the use in the proposed system. The outcome of these research may be applied to many applications including semiconducting microstructures and conducting polymers.