Cu₂O Substrates and Epitaxial Cu₂O/ZnO Thin Film Heterostructures for Solar Energy Conversion

Citation

Darvish, Davis Solomon (2013) Cu₂O Substrates and Epitaxial Cu₂O/ZnO Thin Film Heterostructures for Solar Energy Conversion. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/0KEM-KG56. https://resolver.caltech.edu/CaltechTHESIS:06042013-144822210

Abstract

Future fossil fuel scarcity and environmental degradation have demonstrated the need for renewable, low-carbon sources of energy to power an increasingly industrialized world. Solar energy with its infinite supply makes it an extraordinary resource that should not go unused. However with current materials, adoption is limited by cost and so a paradigm shift must occur to get everyone on the same page embracing solar technology. Cuprous Oxide (Cu₂O) is a promising earth abundant material that can be a great alternative to traditional thin-film photovoltaic materials like CIGS, CdTe, etc. We have prepared Cu₂O bulk substrates by the thermal oxidation of copper foils as well Cu₂O thin films deposited via plasma-assisted Molecular Beam Epitaxy. From preliminary Hall measurements it was determined that Cu₂O would need to be doped extrinsically. This was further confirmed by simulations of ZnO/Cu₂O heterojunctions. A cyclic interdependence between, defect concentration, minority carrier lifetime, film thickness, and carrier concentration manifests itself a primary reason for why efficiencies greater than 4% has yet to be realized. Our growth methodology for our thin-film heterostructures allow precise control of the number of defects that incorporate into our film during both equilibrium and nonequilibrium growth. We also report process flow/device design/fabrication techniques in order to create a device. A typical device without any optimizations exhibited open-circuit voltages Voc, values in excess 500mV; nearly 18% greater than previous solid state devices.

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