Nanowires for Energy

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This proposal is aimed at developing a new solar cell or photovoltaic (PV) technology based on III-V semiconductor nanowires. The highest solar cell efficiencies achieved thus far use III-V semiconductor materials such as gallium arsenide, where research-grade solar cells have exceeded 40% efficiency under concentrated sunlight. These devices employ highly perfect semiconductor thin films in a multi-junction device structure, which consists of sub-cells connected electrically in series. However, these cells are not optimized due to the need to use materials of similar crystal lattice to avoid the generation of defects in the films that would otherwise reduce efficiency. Furthermore, the existing thin film technology is prohibitively expensive due to the materials used such as germanium. To overcome these limitations, this proposal proposes a two-junction cell comprised of nanowires on relatively inexpensive substrates such as silicon. The main advantage of nanowires is the greater freedom to combine materials of different crystal structure to optimize solar cell efficiency. As a result, a nanowire-based solar cell should have optimum efficiency that is comparable to that of commercial thin film cells (>40%), while the former would significantly reduce cost by using cheaper substrates. The efficiency of a nanowire PV device is greatest when the nanowire diameter, length, and spacing are optimized as shown by our recent theoretical work. Therefore, the main focus of this proposal will be the development of ordered nanowire arrays. Scientifically, this proposal will provide key aspects in the design of nanowire-based devices. The proof-of-principle devices produced by this proposal will catalyze a significant worldwide increase within the area of nanostructured III-V/Si solar cells, an area where Canada will then be a leading contender.