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Artificial magnetism is usually investigated in rather complex two- and three-dimensional metamaterials. We propose and experimentally demonstrate non-unity permeability in planar multilayer structures. We further demonstrate the existence of TE hyperbolic modes and magnetic plasmons.
We experimentally demonstrate plasmonic nanostructures that enable dynamic electrical control of the phase and/or amplitude of the plane wave reflected from the nanostructures. We also demonstrate dynamically controlled Purcell enhancement of spontaneous emission of InP quantum dots (QDs) coupled to plasmonic heterostructures.
We study theoretically spontaneous parametric downconversion in nonlinear hyperbolic metamaterials and reveal that a strong enhancement of downconverted photon generation is possible due to the hyperbolic dispersion and modified optical density of states.
We have developed effectively transparent contacts (ETCs) that allow for increased current in heterojunction solar cells. Micro-meter scaled triangular cross-section grid fingers with micro-meter scaled distance redirect light efficiently to the active area of the solar cell and hence, omit losses through reflection at the front finger grid. Furthermore, the grid fingers are placed close together...
We investigate the effect of excitons on charge transport in photovoltaic materials with large exciton binding energies using Cu2O as a model system. We develop a thermodynamic model to estimate the fraction of excitons in Cu2O at quasi-equilibrium and find that over 20% of the generated population of carriers during photovoltaic operation could be excitons. Experiments show the presence of excitons...
We report cryogenic inductively coupled plasma reactive ion etching (ICPRIE) etched tapered silicon microwires are ideal light trapping structures with extremely low (1.08% between 400 nm–1100 nm under normal incidence) reflectivity. We show that these tapered microwire arrays absorb 90.12% of incident light under normal incidence in an effectively 20 μm thick silicon when embedded in a polymer and...
The sub-micrometer absorber regime is currently being explored to reduce materials usage and deposition time while simultaneously increasing device voltages due to increased generated carrier concentration. In order to realize these benefits, the absorption of photons must be maintained or even increased while avoiding detrimental recombination. Reported here are optoelectronic simulations that highlight...
Cu2O is a semiconductor composed of earth — abundant and non-toxic elements that is as a promising photovoltaic material. One of the main issues limiting the efficiency of Cu2O solar cells is the availability of n-type window layers with an appropriate band offset and low interfacial reactivity. In this work, we show the effect of controlling the interface composition on the device properties of a...
Variation of the incident spectrum under real-world illumination conditions can degrade the performance of series connected multijunction solar cells that are optimized for performance under the AM1.5D standard spectrum. Current approaches to correct for this factor and estimate energy production for deployed systems require large amounts of field data and are not useful for evaluating prospective...
By the mid-17th century, numerous scientists—notably including Hooke and Gallileo—had developed transparent ground lenses and applied them in the construction of compound optical microscopes. This development revolutionized the contemporary understanding of the natural world by, for example, enabling the imaging of blood cells and microbes. Ever since this now bygone era of fantastic development...
We experimentally demonstrate spectrally broad (λ0=1200–1800 nm) in-plane negative diffraction of SPPs in an array of plasmonic channel waveguides with negative mutual coupling resulting in negative refraction on the array's interface and refocusing in an adjacent metal layer.
We experimentally demonstrate an ultracompact PlasMOStor, a plasmon slot waveguide field-effect modulator based on a transparent conducting oxide active region, as illustrated in Fig. 1. By electrically modulating the conducting oxide material deposited into the gaps of highly confined plasmonic slot waveguides, we demonstrate field-effect dynamics giving rise to modulation with high dynamic range...
Cu2O is a p-type semiconductor that has demonstrated attractive photovoltaic properties, but its efficiencies have been limited by surface instability and lack of high quality thin films. In this work, plasma-assisted molecular beam epitaxy is used to precisely control film orientation and interface chemistry of Cu2O heterostructures. Thin films of Cu2O are deposited by MBE onto thin films of Pt and...
We investigate a spectrum-splitting design, the polyhedral specular reflector, for an ultra-high efficiency module (>50%). The design employs a series of multilayer dielectric stack filters to divide the incident spectrum onto seven independently connected subcells. We optimized the geometry and components of the design through coupled wave-optics, device physics, electrical circuit, and ray tracing...
The II–IV-nitrides are an alloy series analogous to the well-characterized III-nitrides, where a Group II and Group IV element replace the Group III element. We report on the fabrication and structural and optoelectronic characterization of earth-abundant II–IV-nitrides: ZnSnxGe1−xN2. The sputtered thin-films show potential for ZnSnxGe1−xN2 to be tunable semiconductor photovoltaic absorber materials.
Cu2O is a p-type semiconductor with desirable bulk properties for photovoltaics. However, the lack of an n-type dopant and surface instability have hindered the development of a high efficiency Cu2O device. In this work, the floating zone method is used to grow high quality single crystals of Cu2O in order to controllably study the interfacial reactions between Cu2O and its heterojunction partners...
The world record efficiency and open circuit voltage for crystalline silicon solar cells are held by a-Si/Si heterojunction devices. While a-Si provides excellent surface passivation, these heterojunction devices are limited by non-ideal optical and electronic properties. Gallium phosphide is a candidate material for replacing a-Si in a heterojunction device, promising lower parasitic absorption and...
We discuss ‘full spectrum’ photovoltaic modules that leverage low-cost III-V compound semiconductor cells, efficient optics and unconventional fabrication/assembly methods, and discuss advances in photoelectrochemical water-splitting with high efficiency.
We describe nanophotonic design approaches for broadband light management including i) crossed-trapezoidal Si structures ii) Si photonic crystal superlattices, and iii) tapered and inhomogeneous diameter III-V/Si nanowire arrays.
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