An engineered enhancement in short-circuit current density and energy conversion efficiency in amorphous silicon p-in solar cells is achieved via improved transmission of electromagnetic radiation arising from forward scattering by surface plasmon polariton modes in Au nanoparticles deposited above the amorphous silicon film. For a Au nanoparticle density of ϳ3.7ϫ 10 8 cm −2 , an 8.1% increase in short-circuit current density and an 8.3% increase in energy conversion efficiency are observed. Finite-element electromagnetic simulations confirm the expected increase in transmission of electromagnetic radiation at visible wavelengths, and suggest that substantially larger improvements should be attainable for higher nanoparticle densities.
Experimental characterization and finite-element numerical simulations of the electromagnetic interaction between Au nanoparticles positioned atop a Si pn junction photodiode and incident electromagnetic plane waves have been performed as a function of wavelength. The presence of the Au nanoparticles is found to lead to increased electromagnetic field amplitude within the semiconductor, and consequently increased photocurrent response, over a broad range of wavelengths extending upward from the nanoparticle surface plasmon polariton resonance wavelength. At shorter wavelengths, a reduction in electromagnetic field amplitude and a corresponding decrease in photocurrent response in the semiconductor are observed. Numerical simulations reveal that these different behaviors are a consequence of a shift in the phase of the nanoparticle polarizability near the surface plasmon polariton wavelength, leading to interference effects within the semiconductor that vary strongly with wavelength. These observations have substantial implications for the optimization of device structures in which surface plasmon polariton resonances in metallic nanoparticles are exploited to engineer the performance of semiconductor photodetectors and related devices.
The influence of electromagnetic scattering by Au and silica nanoparticles placed atop silicon photovoltaic devices on absorption and photocurrent generation has been investigated. The nanoparticles produce substantial increases in power transmission into the semiconductor and consequently photocurrent response from ϳ500 toϾ 1000 nm. Increases in power conversion efficiency under simulated solar irradiation of up to 8.8% are observed experimentally, and numerical simulations provide quantitatively accurate predictions of these observed enhancements. Additional simulations indicate that these concepts can be applied to a broad range of photovoltaic device structures, including those based on low-index materials for which conventional antireflection coatings are problematic.
We report on the improved performance of InP / InGaAsP quantum-well waveguide solar cells via light scattering from deposited dielectric or metal nanoparticles. The integration of metal or dielectric nanoparticles above the quantum-well solar cell device is shown to couple normally incident light into lateral optical propagation paths, with optical confinement provided by the refractive index contrast between the quantum-well layers and surrounding material. With minimal optimization, short-circuit current density increases of 12.9% and 7.3% and power conversion efficiency increases of 17% and 1% are observed for silica and Au nanoparticles, respectively.
We present a new class of nanoscale plasmonic sources based on subwavelength dielectric cavities embedded in a metal slab. Exploiting the strong dispersion near the Fabry-Perot resonance in such a resonator, we control the phase and the amplitude of the generated plasmons at the subwavelength scale. As an example, we present a subwavelength unidirectional plasmonic antenna utilizing interference between two plasmonic cavity sources with matched phase and amplitude.Surface plasmons polaritons (SPPs) are collective excitations of electrons coupled to an electromagnetic field at the interface between a dielectric and a metal.1 Their evanescent nature along the normal to the metal/dielectric interface allows subwavelength confinement that can be significantly smaller than diffraction limited optical waves in bulk media. SPPs, therefore, are ideal candidates for the construction of subwavelength optical devices. In the past few years, SPPs have also been identified to be the major physical mechanism involved in the extraordinary transmission of light (ETL) through metal films with subwavelength holes which was first reported by Ebbesen et al. 2,4 Subsequent studies have been made on uniform periodic arrays of holes, slits, and more complex shapes fabricated in metallic films. Those studies demonstrate that one can take advantage of the interference between plasmons generated on metal films by uniform periodic sources (e.g., slits or holes in metal films) to, for instance, focus or disperse light, 5,6 or realize ETL. Naturally, for flexible control and manipulation of light by such metal films it is necessary to evolve beyond the uniform periodic sources in refs 2-7 and introduce the rich possibilities afforded by nonuniform source films. When light enters a subwavelength dielectric structure in a metallic film, a significant fraction, if not all, of the light propagates through the film as surface plasmons that are confined at the metal/dielectric interfaces. For example, transverse magnetic (TM) polarized light impinging on a silver film containing air gaps gives rise to waves known as gap plasmons (GPs), whose properties are closely related to the dimensions of the gaps: the smaller the gap width, the larger the wavenumber of the GP. 11,12 This way, one can design sources of plasmons with arbitrary phase by adjusting the width of the gap. Similarly, one can fill the air gaps with different dielectrics hence inducing an optical path length between the generated plasmons. 8,10 Those two approaches are quite inflexible and practically hard to fabricate.In order to realize surface plasmon sources with chosen phase and amplitude, our approach utilizes the gap plasmon dispersion relation along with Fabry-Perot (FP) resonances in a cavity. 13,14 Air gaps in metal films typically display lowefficiency FP resonance 13 that, as we explain later, can be increased by introducing highly reflective "mirrors" on both sides of the metal film. Sharper resonance results in longer propagation of the GPs in the gaps due to con...
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