title: Direct-bandgap epitaxial core-multishell nanopillar photovoltaics featuring subwavelength optical concentrators.
abstract: Semiconductor nanomaterials have recently fueled numerous photonic scientific fields. Arrays of nanopillars (NPs) have been examined by the photovoltaic (PV) community as highly efficient solar absorbers, with potential material/cost reductions compared to planar architectures. Despite modeled predictions, experimental efficiencies are limited by surface recombination and poor light management, once integrated in a practical PV device. In this Letter, we correlate optoelectronic modeling with experimental results for direct-bandgap arrays of core-multishell GaAs NPs grown by selective area, catalyst-free epitaxy and capped by epitaxial window layers, with efficiencies of 7.43%. Electrically, improved open-circuit voltages are yet partly affected by residual surface state density after epitaxial passivation. Optically, dome-shaped indium-tin-oxide (ITO) top electrode functions as a two-dimensional (2-D) periodic array of subwavelength lenses that focus the local density of optical states within the NP active volume. These devices provide a path to high-efficiency NP-based PVs by synergistically controlling the heteroepitaxy and light management of the final structure.
authors.affiliation: Electrical Engineering Department, University of California at Los Angeles, Los Angeles, California 90095, United States. giacomomariani@ucla.edu
authors.forename: Giacomo
authors.initials: G
authors.lastname: Mariani
authors.forename: Zhengliu
authors.initials: Z
authors.lastname: Zhou
authors.forename: Adam
authors.initials: A
authors.lastname: Scofield
authors.forename: Diana L
authors.initials: DL
authors.lastname: Huffaker
mesh_terms: D001152:Arsenicals / Q000737:chemistry*; D004566:Electrodes; D005708:Gallium / Q000737:chemistry*; D008027:Light; D036103:Nanotechnology; D045663:Quantum Dots / Q000737:chemistry*; D012993:Solar Energy; D017971:Tin Compounds / Q000737:chemistry
chemical_list: D001152:Arsenicals; D017971:Tin Compounds; C043055:gallium arsenide; C109984:indium tin oxide; D005708:Gallium