Mahdi Farrokh Baroughi

Geometry dependence of field enhancement in 2D metallic photonic crystals

Geometry dependence of surface plasmon resonance of 2D metallic photonic crystals (PCs) was assessed using rigorous 3D finite difference time domain analysis. PCs of noble metallic rectangular and cylindrical nanopillars in square and triangular lattices on thick noble metal film were simulated for maximum field enhancement. It was found that the period, size and thickness of the nanopillars can be tuned to excite of surface plasmons at desired wavelengths in visible and near-infrared ranges. Maximum electric field enhancement near the nanopillars was found to be greater than 10X. The detail analysis of PCs tuned for 750 nm wavelength showed that thickness of nanopillars was the most sensitive parameter for field enhancement, and triangular lattice PCs had the wider enhancement bandwidth than square lattice PCs. Results showed that these PCs are sensitive with incident angle (theta) but not with polarization angle (phi).

Efficient, uniform, and large area microwave magnetic coupling to NV centers in diamond using double split-ring resonators.

We report on the development and utilization of a double split-ring microwave resonator for uniform and efficient coupling of microwave magnetic field into nitrogen-vacancy (NV) centers in a diamond over a mm(2) area. Uniformity and magnitude of delivered microwave field were measured using the Rabi nutation experiment on arrays of diamond nanowires with ensemble NV centers. An average Rabi nutation frequency of 15.65 MHz was measured over an area of 0.95 × 1.2 mm, for an input microwave power of 0.5 W. By mapping the Rabi nutation frequency to the magnetic field, the average value of the magnetic field over the aforementioned area and input microwave power was 5.59 G with a standard division of 0.24 G.

Plasmon resonance modes in two-dimensional arrays of metallic nanopillars

Surface plasmon polaritons (SPPs) and localized plasmon resonance modes in two-dimensional arrays of silver nanopillars on silver surface were analyzed using the three-dimensional finite-difference time domain method. What we believe to be a new type of plasmon resonance modes at oblique incident angle for p-polarized light was observed in two-dimensional arrays of silver nanopillars in a square lattice. This resonance mode is associated with two SPP-like electric field patterns along the metal surface. We found that this resonance mode is localized and excited by the transverse polarization mode of nanopillars. Using Poynting vector plots, it was observed that the plasmon resonances in arrays of nanopillars are always associated with large energy cyclones near the nanopillars leading to light absorption.

Cost-Effective, Silicon-Based Solar Cells: Material and Technology Issues

Affordability is the key to any renewable energy technology in becoming a viable alternative to conventional energy technology. Solar photovoltaics (PV) is a promising and environment-friendly energy conversion technique, experiencing steady market growth. Cost reduction of PV cells relies largely on the use of low-cost silicon materials which tend to compromise the device performance. This underscores the need for new, material-specific process technologies to be used in order to achieve an acceptable

Design, fabrication, and characterization of a plasmonic upconversion enhancer and its prospects for photovoltaics

/Wp. In this paper, first an overview of different techniques for the fabrication of low-cost silicon will be presented. We highlight the need to modify the processing technology while using defective, cost-effective Si substrates. This is followed by the description of research efforts on the development of a cost-effective heterojunction cell fabrication technology, as well as the results on the simplified process.

Modeling of trap assisted interfacial charge transfer in dye sensitized solar cells

Abstract. The design, fabrication, and characterization of an upconversion-luminescence enhancer based on a two-dimensional plasmonic crystal are described. Full-wave finite-difference time domain analysis was used for optimizing the geometrical parameters of the plasmonic crystal for maximum plasmon activity, as signified by minimum light reflection. The optimum design produced >20× enhancement in the average electromagnetic field intensity within a one-micron-thick dielectric film over the plasmonic crystal. The optimized plasmonic upconverter was fabricated and used to enhance the upconversion efficiency of sodium yttrium fluoride: 3% erbium, 17% ytterbium nanocrystals dispersed in a poly(methylmethcrylate) matrix. A thin film of the upconversion layer, 105 nm in thickness, was spin-coated on the surface of the plasmonic crystal, as well as on the surfaces of planar gold and bare glass, which were used as reference samples. Compared to the sample with a planar gold back reflector, the plasmonic crystal showed an enhancement of 3.3× for upconversion of 980-nm photons to 655-nm photons. The upconversion enhancement was 25.9× compared to the same coating on bare glass. An absorption model was developed to assess the viability of plasmonically enhanced upconversion for photovoltaic applications.

Design and Simulation of Photonic Crystal Based Polarization Converter

This paper presents a model for charge transport in dye sensitized solar cells based on the physics of electron capture, electron emission, oxidation, and reduction processes mediated by deep interfacial trap states at TiO2/dye/electrolyte interfaces. This model suggests that electron back injection from the conduction band of TiO2 to electrolyte is due to trapping of conduction band electrons by deep states followed by reduction processes at the interface. The simulated dark IV, illuminated IV, and quantum efficiency characteristics of dye sensitized solar cells based on this model are consistent with experimental results.

Enhancement of electromagnetic field intensity by metallic photonic crystal for efficient upconversion

A periodic asymmetrically loaded photonic-crystal (PC) based polarization converter has been designed and fabricated. The polarization converter structure consists of a single defect line square hole PC slab waveguide with asymmetrically loaded top layer. The design methodology consists of finding the birefringence induced by geometrical asymmetry through full-wave modal analysis. The proposed design methodology can be extended to arbitrary air hole shape photonic-crystal-based polarization converter. The length and total number of top loaded layers are determined upon full-wave modal analysis. The thickness of the loaded top layer has been optimized to provide wideband and low loss polarization conversion. The optimized thickness of the top loaded layer is 0.2a for which polarization conversion takes place over the propagation distance of 13lambda0. For this distance, the coupling efficiency higher than 90% is achieved within the normalized frequency band of 0.258-0.267 corresponding to 584-604.5 GHz for the design example presented in III.

Unified electronic charge transport model for organic solar cells

2D arrays of cylindrical and rectangular gold nanopillars in square and triangular lattice were investigated for maximum field intensity enhancement above the metal dielectric interface. 3D-FDTD method was used for investigation and design of metallic photonic crystal. Photonic crystal was designed for maximum electromagnetic field intensity enhancement in infrared radiation centered at 980 nm wavelength. It was found that gold nanopillars of thickness 70nm, diameter 310nm and periodic in 620nm enhances the electromagnetic intensity by 100 times above the metallic nanopillars by exciting surface plasmon resonance. Enhancement of near-field intensity by two orders of magnitude is the promising way to increase the upconversion of infrared radiation by rare earth doped nanoparticles, such as NaYF4:Er,Yb.

FDTD simulation of metallic gratings for enhancement of electromagnetic field by surface plasmon resonance

This paper provides a comprehensive modeling approach for simulation of electronic charge transport in excitonic solar cells with organic and organic/inorganic structures. Interaction of energy carrying particles (electrons, holes, singlet excitons, and triplet excitons) with each other and their transformation in the bulk of the donor and acceptor media as well as the donor/acceptor interfaces are incorporated in form of coupling matrices into the continuity equations and interface boundary conditions. As a case study, the model is applied to simulate an organic bilayer photovoltaic (PV) device to quantify the effects of photo generation, recombination coefficient, carrier mobility, and electrode work function on its PV characteristics. The study proves that electron-hole recombination at the donor/acceptor interface is the dominant mechanism that limits open circuit voltage of the device.