Si Microwire Array Photoanodes for Artificial Photosynthetic Devices

Citation

Santori, Elizabeth Anne (2013) Si Microwire Array Photoanodes for Artificial Photosynthetic Devices. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/5YDX-5Y66. https://resolver.caltech.edu/CaltechTHESIS:11172012-135639556

Abstract

To realize the large-scale deployment of solar power, new materials and strategies must be developed for the fabrication of economical and sustainable artificial photosynthetic devices. These systems have multiple constraints, which are typically met by employing expensive, multi-junction solar cells coupled to noble metal catalysts. However, to supply and store power on a global, terawatt scale, these technologies must shift towards utilizing abundant elements and low-cost deposition techniques, while maintaining device efficiency. Driven by these challenges, this thesis presents achievements in Si microwire arrays to realize cost competitive and sustainable artificial photosynthetic devices.

The device performance of Si microwire arrays, a thin-film photovoltaic technology, was investigated using photoelectrochemical methods. Both n-type and lightly doped Si microwire arrays demonstrated improved performance as photoanodes, and may be used in an artificial photosynthetic device to perform oxidative reactions. In addition, lightly doped Si microwire arrays operating under high-level injection conditions achieved performance comparable to that of optimally doped p-type Si microwire array photocathodes, with V_oc values exceeding 450 mV and carrier collection efficiencies of ~ 0.85. A model of these devices operating under high-level injection conditions was developed, using finite-element device physics simulations. These simulations predicted that the carrier collection efficiencies of the devices should deviate from unity, even for minority-carrier diffusion lengths greater than the radius. Such behavior was confirmed by experimental internal quantum yield measurements, reaffirming that these devices are limited by axial transport of carriers along the length of the wire. However, optimized arrays have the potential to generate voltages that exceed those generated by arrays operating under low-level injection conditions. Such studies offer increased understanding of the performance of structured, concentrator photovoltaics and considerations for structuring lightly doped materials on the nano- and microscale.

Thesis Files