Mohamed Amara

Reassessment of the intrinsic carrier density temperature dependence in crystalline silicon

The intrinsic carrier density ni of crystalline silicon is an essential parameter for the simulation of electrical and thermal behavior of silicon devices. At 300u2009K, a value of ni=9.65×109u2009cm−3 has been determined by extensive experimental studies. However, the temperature dependence of this parameter remains to be verified. In this work, we propose a new expression ni=1.541×1015T1.712exp(−Eg0/(2kT)) thanks to an updated fit of experimental data. Polynomial fits of (mdc*/m0)32 and (mdv*/m0)32 are also proposed to model NC and NV.

In-Depth Analysis of Heat Generation in Silicon Solar Cells

The knowledge of the temperature of solar cells and its dependence on its parameters such as wafer thickness and resistivity, optical treatment, etc., give a new opportunity to enhance the efficiency of the energy conversion in operating conditions. A 1-D numerical model is presented to simulate heat transfer and electrical characteristics of p-n silicon solar cells. This model encompasses every heat mechanisms occurring in a solar cell. Three of them are prevailing: thermalization, recombination of carriers, and Joule effect. The total amount of generated heat depends on the applied bias on the solar cell. It prevents the application of the principle of superposition when thermal issues are considered. The sensitivity of the solar cell to the variation of solar spectral distribution is studied in order to highlight the difference between a standard analysis and the one from this multiphysics model.

Assessing the Efficiency of Advanced Multijunction Solar Cells in Real Working Conditions: A Theoretical Analysis

Multijunction (MJ) solar cells are currently seen as one of the most promising options toward achieving solar energy to electricity conversion efficiencies exceeding 50%. The detailed balance theory provides a practical tool for tailoring MJ solar cells, taking several strong assumptions regarding the spectral input or the cell temperature. However, solar cells in real working operation may meet conditions that differ significantly from the ideal conditions for which they were designed. Assessing the extent to which advanced MJ solar cell architectures are able to withstand changes in the operating conditions is thus crucial toward ensuring an efficient use of MJ solar cells in real working operation. In this paper, the sensitivity of current-constrained MJ solar cells to operating conditions was studied by quantifying the decrease in the conversion efficiency associated with a change in the spectral input, the illumination level, and the cell working temperature. The sensitivity of MJ solar cells to the spectral content of the light was shown to be significant for cell architecture involving four subcells and more. On the contrary, the gain in efficiency achieved by tailoring the combination of bandgap to a specific value of the working temperature or the illumination level was demonstrated to be low. The implications for future generations of MJ solar cells comprising up to ten subcells are also addressed.

Effects of non-ideal losses on the optimal bandgap arrangement of multi-junction solar cells comprising up to 5 subcells

The present work aims at better understanding the effects of the different limiting mechanisms on the performance of multi-junction stacks comprising up to 5 subcells, and to assess the extent to which the iso-efficiency curves derived with the detailed balance model are affected by these non-ideal losses. In light of these results, further discussions and analysis will be carried out in order to understand which arrangements of bandgaps could potentially achieve practical conversion efficiency approaching the theoretical limit.

Impact of the bias on the temperature of silicon solar cells under operating conditions

Currently, the temperature of an illuminated solar cell is thought independent of its bias. This assumption allows the application of the principle of superposition. However, the temperature dependence of the solar cell with respect to its bias can be shown to induce a departure from the principle of superposition with the aid of rigorous electro-thermo-radiative simulations. This dependence limits the validity of the principle of superposition to solar cell where the temperature is controlled. We further demonstrate that the temperature at the maximum power point is close to the lowest temperature of the cell as a function of the bias. In order to be as close as possible to the operating conditions of a solar cell, it is suggested to determine the nominal operating cell temperature at the maximum power point instead of the open circuit conditions as defined in the ASTM standard and to optimize solar cells for the temperature at the maximum power point.