S. Abdellatif

Nanowire photovoltaic efficiency enhancement using plasmonic coupled nano-fractal antennas.

We suggest the use of nano-fractal antennas for plasmonic coupling to enhance nanowire (NW) photovoltaic power conversion efficiency. Silicon radial pn junction NWs positioned inside Apollonian and Sierpinski nano-fractal antennas are simulated with different topologies and NW lengths. An enhancement in power conversion efficiency ranging from 12% to up to 24% over the same NW without antenna case is achieved.

Spectral and spatial distribution effects on nanowires inside nanoring optical antennas for photovoltaic arrays

The effect of enclosing a nanowire (NW) radial pn junction photovoltaic (PV) element inside a nanoring optical antenna to enhance the electric field in the near field region has been investigated. Five different materials for the NW (Si, Ge, GaAs, GaInP and InGaAs) have been selected to maximize the absorbed solar spectrum. In addition, the position and diameter of the NW are varied through a random distribution to optimize the power conversion efficiency. Results show that the ring antenna geometry and the NW random spatial distribution are effective in both spectral widening and field concentration which result in an increase of the cell conversion efficiency.

Enhancing the absorption capabilities of thin-film solar cells using sandwiched light trapping structures

A novel structure for thin-film solar cells is simulated with the purpose of maximizing the absorption of light in the active layer and of reducing the parasitic absorption in other layers. In the proposed structure, the active layer is formed from an amorphous silicon thin film sandwiched between silicon nanowires from above and photonic crystal structures from below. The upper electrical contact consists of an indium tin oxide layer, which serves also as an antireflection coating. A metal backreflector works additionally as the other contact. The simulation was done using a new reliable, efficient and generic optoelectronic approach. The suggested multiscale simulation model integrates the finite-difference time-domain algorithm used in solving Maxwells equation in three dimensions with a commercial simulation platform based on the finite element method for carrier transport modeling. The absorption profile, the external quantum efficient, and the power conversion efficiency of the suggested solar cell are calculated. A noticeable enhancement is found in all the characteristics of the novel structure with an estimated 32% increase in the total conversion efficiency over a cell without any light trapping mechanisms.

Simulating the dispersive behavior of semiconductors using the Lorentzian-Drude model for photovoltaic devices.

Unique light-trapping structures that improve the efficiency of thin-film solar cells require advanced computational methods that can simulate the propagation of light through the thickness of each material in the solar cell. The simulations community that uses the Lorentz-Drude (LD) model cannot precisely simulate the propagation of light through the entire spectrum of the Sun, due to the difficulty in extrapolating the coefficients of each solar cell material. In this paper, a new technique for modeling dispersive and absorptive material over the Suns entire wavelength range (200-1700 nm) using the LD model is suggested. The new numerical models are used for simulating light propagation through various one-dimensional light-trapping structures, including metal backreflectors and distributed Bragg reflectors. All the numerical simulation results show agreement with previously published theoretical and experimental results. The proposed simulation technique will help the simulations community in using the LD model to simulate the propagation of light in solar cells more accurately.

Comprehensive study of various light trapping techniques used for sandwiched thin film solar cell structures

Thin film solar cells (TFSCs) where first introduced as a low cost alternative to conventional thick ones. TFSCs show low conversion efficiencies due to the used poor quality materials having weak absorption capabilities and to thin absorption layers. In order to increase light absorption within the active layer, specially near its absorption edge, photon management techniques were proposed. These techniques could be implemented on the top of the active layer to enhance the absorption capabilities and/or to act as anti-reflecting coating structures. When used at the back side, their purpose is to prevent the unabsorbed photons from escaping through the back of the cell. In this paper, we coupled the finite difference time-domain (FDTD) algorithm for simulating light interaction within the cell with the commercial simulator Comsol Multiphysics 4.3b for describing carrier transports. In order to model the dispersive and absorption properties of various used materials, their complex refractive indices were estimated using the Lorentzian-Drude (LD) coefficients. We have calculated the absorption profile in the different layers of the cell, the external quantum efficiency and the power conversion efficiency achieved by adding dielectric nanospheres on the top of the active layer. Besides that, the enhancement observed after the addition of dielectric nanospheres at the back side of the active layer was computed. The obtained results are finally compared with the effects of using textured surface and nanowires on the top in plus of cascaded 1D and 2D photonic crystals on the back.