Ahmad Mohammadi

Persian Gulf University | PGU · Department of physics

The increase in optical absorption in organic solar cells based on poly (3-hexylthiophene): phenyl-C61-butyric acid methyl ester (P3HT:PC61BM), is examined in this study utilizing the finite difference time domain method and Lumerical software to evaluate field distribution and light absorption in the active layer in terms of wavelength. The plasmo...

In this paper, the light absorption in the active layer of polymer solar cells (OPV) by using plasmonic nanocrystals with a hexagonal lattice structure is investigated. To study the relationship between the performance of the OPV solar cell and its active layer, a three-dimensional model of its morphology is utilized. Therefore, the three-dimension...

An efficient method inspired by the traditional body of revolution finite-difference time-domain (BOR-FDTD) method is developed to solve the Schrodinger equation for rotationally symmetric problems. As test cases, spherical, cylindrical, cone-like quantum dots, harmonic oscillator, and spherical quantum dot with hydrogenic impurity are investigated...

We used the finite difference time domain method to calculate scattering spectra for a multilayer nanoshell (MNS) consisting of a gold core, a molecular layer and a gold shell. The effects of geometrical parameters of the multilayer nanoshell (MNS) such as size, aspect ratio, the thickness of the shell and middle layer on the scattering properties...

In this paper, the light absorption the active layer of polymer polymer solar cells (OPV) by using plasmonic nanocrystals with hexagonal lattice is investigated. To study the relation between the performance of the OPV solar cell and its active layer, a three-dimensional model for its morphology is utilized. Therefore, the three-dimensional (3D) fi...

In this work, we first use the finite-differential time-domain (FDTD) to calculate the eigenenergies and eigenfunctions of a three dimensional (3D) cylindrical quantum wire. We assume that the inside of the wire is at zero potential. But, the outside of the wire has been chosen at different potentials as infinite and finite values. This is a true 3...

Utilizing the finite difference time domain (FDTD) method, energy eigenvalues of spherical, cylindrical, pyramidal and cone-like quantum dots are calculated. To do this, by the imaginary time transformation, we transform the schrödinger equation into a diffusion equation. Then, the FDTD algorithm is hired to solve this equation. We calculate four l...

The minimization of the reflection of Si substrates is analyzed for the use of photovoltaic applications. Antire-flection coatings consisted of both bulk and nanostructured thin film and ITO over a broad spectral range of 400-1000 nm are optimized. The genetic algorithm and the transfer matrix method are applied and the thickness of layer varied, w...

Plasmonic gold nanocones offer outstanding possibilities to control light-matter interaction at the nanoscale. For instance, they can be exploited to modify the photonic environment around a single emitter for tuning its quantum efficiency and radiative decay rate, as well as the angular distribution and polarization of the emitted photons. However...

We discuss the rules for designing nanostructured plasmonic backcontact of thin-film crystalline silicon solar cells using two-dimensional finite-difference time-domain (2D-FDTD) method. A novel efficient quasi-periodic plasmonic nanograting is designed. Numerical calculations demonstrate that broadband and polarization-insensitive absorption enhan...

The dramatic advances of nanotechnology experienced in recent years enabled us to fabricate optical nanostructures or nano-antennas that greatly enhance the conversion of localised electromagnetic energy into radiation and vice versa. Nano-antennas offer the required improvements in terms of bandwidth, interaction strength and resolution for combin...

We investigate light scattering under nanofocusing in the context of coherent spectroscopy. We discuss the different mechanisms that may enhance the signal in extinction and how these depend on nanofocusing as well as on the probed system. We find that nanofocusing may improve the detection sensitivity by orders of magnitude under realistic conditi...

We investigate the properties of finite gold nanocones as optical antennas for enhancing molecular fluorescence. We compute the modification of the excitation rate, spontaneous emission rate, and quantum efficiency as a function of the nanocone base and length, showing that the maximum field and fluorescence enhancements do not occur for the same n...

We compute the decay rates of emitters coupled to spheroidal nanoantennas made of gold, copper, silver, and aluminum. The spectral position of the localized surface plasmon-polariton resonance, the enhancement factors and the quantum efficiency are investigated as a function of the aspect ratio, background index and the metal composing the nanoante...

Nanoantennas made of spheroidal metal nanoparticles are studied as a function of several parameters, namely aspect ratio, volume, background index and metal. Single nanospheroids are analysed using the polarisability theory with radiative and depolarisation corrections, while double spheroids are investigated using the finite-difference time-domain...

We compute the radiative decay rate and the quantum efficiency for an emitter coupled to gold nanorods and nanospheroids using the body-of-revolution finite-difference time-domain method. We study these quantities as a function of the nanoparticle aspect ratio and volume, showing that large enhancements can be achieved with realistic parameters. Mo...

We have extended the contour-path effective-permittivity (CP-EP) finite-difference time-domain (FDTD) algorithm by A. Mohammadi et al., Opt. Express 13, 10367 (2005), to linear dispersive materials using the Z-transform formalism. We test our method against staircasing and the exact solution for plasmon spectra of metal nanoparticles. We show that...

In this paper, we present an efficient effective permittivity treatment for the two-dimensional Finite- Difference Time-Domain (2D-FDTD) method that can be applied to dielectric interfaces. Various issues related to simulation arrangements are discussed based on the 60� photonic crystal (PhC) waveguide bend as a test case. The transmission, obtaine...

In this paper, we present an efficient effective permittivity treatment for the two-dimensional Finite-Difference Time-Domain (2D-FDTD) method that can be applied to dielectric interfaces. Various issues related to simulation arrangements are discussed based on the 60 photonic crystal (PhC) waveguide bend as a test case. The transmission, obtained...

We investigate the accuracy of the two-dimensional Finite-Difference Time-Domain (FDTD) method in modelling Surface Plasmon Polaritons (SPPs) in the case of a single metal-dielectric interface and of a thin metal film showing that FDTD has difficulties in the low-group-velocity region of the SPP. We combine a contour-path approach with Z transform...

Effective permittivities for the two-dimensional Finite- Difference Time-Domain (FDTD) method are derived using a contour path approach that accounts for the boundary conditions of the electromagnetic field at dielectric interfaces. A phenomenological formula for the effective permittivities is also proposed as an effective and simpler alternative...