Analysis of photocurrent in the i-layer of GaAs-based n–i–p solar cell

A numerical investigation of the intrinsic layer effect on the improvement of GaAs n–i–p solar cell performances is presented. Solution of Poisson's equation together with continuity equations for electrons and holes allows the determination of carrier's density, electric field and recombination profiles within the i-layer. The analysis examines the effect of i-layer thickness on the electric field, recombination rate and collection efficiency. It is found that increasing the i-layer thickness increases the absorption while it reduces the electric field and increases the recombination rate. The three competing parameters have to be monitored simultaneously so as to obtain an optimal thickness. To achieve this, the variation of the total photocurrent is used as indicator. The photocurrent shows a sharp increase in the domain of very thin i-layers (<0.5 μm) then a saturation is reached for thicker layers (>1 μm), the simulation is performed for thicknesses up to 2 μm.     

High efficiency all‐GaAs solar cell

The reduction of surface recombination in GaAs solar cells is known to be a major concern for photovoltaic cells designers. A common technique used to reduce this effect is to cover the GaAs surface with a wide band gap window layer, therefore the creation of a heterojunction. To avoid a heterojunction with its inconveniences; interface surface states, poor photon absorption in addition to the technological exigencies, one can use an all‐GaAs solar cell. In this type of structure, a thin highly doped layer is created at the surface known as a front surface field (FSF). The main role of an FSF layer is to reduce the effect of front surface recombination and the enhancement of light‐generated free carriers' collection. This is achieved by the drastic reduction of the effective recombination at the emitter upper boundary. In this work, a simple analytical model is used to simulate the influence of the FSF layer on GaAs solar cell parameters; photocurrent, open circuit voltage and energy conversion efficiency. The effects of the FSF layer doping density and its thickness on the cell performance are discussed by using computed results. Copyright © 2010 John Wiley & Sons, Ltd.     

A Predictive Model of the Optimal Tool Edge Geometry for Veneer Cutting Processes

Abstract

Veneer cutting is a specific machining process, where the chip is the final product. The objective of this article is to investigate on the optimal tool edge geometry, using particle swarm optimization (PSO) algorithm, to obtain the desired veneer thickness. The challenge is to maintain the best quality of veneer product with the control of pre-splitting condition and thickness variation. Numerical results obtained from PSO algorithm are compared and verified with the experimental ones. The proposed model allows us to predict the characteristic tool angles for different chip thicknesses and friction coefficients. For chip thickness range greater than 2?mm, the presplitting condition is no longer satisfied, as in the case of rotary peeling veneer, the need of using pressure bar becomes primordial.     

Hydrodynamic study involving a maxblend impeller with yield stress fluids

In the present study, the hydrodynamic characteristics of the Maxblend impeller have been investigated. A commercial CFD package (CFX 12.0) was used to solve the 3D hydrodynamics and to characterize the flow patterns at every point. A shear thinning fluid with yield stress was modeled in the laminar regime and transition regime. The study focused on the effect of fluid rheology, agitator speed, impeller clearance from the tank bottom and blade size on the fluid flow and power consumption. Predictions have been compared with literature data and a satisfactory agreement has been found.     

Effect of the front surface field on GaAs solar cell photocurrent

It is well established that the inclusion of a high–low junction at the back of a solar cell or the so-called back surface field (BSF), improves its performance. In the other hand, if the same structure is placed at the front of the cell as high–low junction emitter, front surface field (FSF), a notable amelioration is observed. In this work, a simulation of the influence of the FSF on GaAs solar cell spectral response and photocurrent is carried out. The model is based on a simple analytical approach. The most important role of an FSF layer is the enhancement of light-generated free carriers’ collection, and this property is primarily responsible for the increase of the short-wavelength quantum efficiency. This is achieved by the drastic reduction of the effective recombination at the emitter upper boundary. The effects of the FSF layer doping concentration and its thickness on the cell performance are discussed by using the computed results.