title: Optimization and analysis of 3D nanostructures for power-density enhancement in ultra-thin photovoltaics under oblique illumination.
abstract: Nanostructures have the potential to significantly increase the output power-density of ultra-thin photovoltaic devices by scattering incident sunlight into resonant guided modes. We applied a modified version of the direct-binary-search algorithm to design such nanostructures in order to maximize the output power-density under oblique-illumination conditions. We show that with appropriate design of nanostructured cladding layers, it is possible for a 10nm-thick organic absorber to produce an average peak power-density of 4 mW/cm² with incident polar angle ranging from -90° to 90° and incident azimuthal angle ranging from -23.5° to 23.5°. Using careful modal and spectral analysis, we further show that an optimal trade-off of absorption at λ~510 nm among various angles of incidence is essential to excellent performance under oblique illumination. Finally, we show that the optimized device with no sun tracking can produce on an average 7.23 times more energy per year than that produced by a comparable unpatterned device with an optimal anti-reflection coating.
authors.forename: Bing
authors.initials: B
authors.lastname: Shen
authors.forename: Peng
authors.initials: P
authors.lastname: Wang
authors.forename: Rajesh
authors.initials: R
authors.lastname: Menon