Numerical simulation of the performance of solar cells formed by nanostructures based on II-VI semiconductors (Simulation numérique des performances des cellules solaires formées par des nanostructures à base des semi-conducteurs II-VI).

Abstract

In the recent years, the use of II-VI semiconductors thin-films like CdTe and CdS in solar cells has significantly augmented due to high device efficiency, stability in the performance, and cost-effectiveness. In this thesis, a CdS/CdTe solar cell has been investigated employing 2-dimensional numerical simulations using TCAD Silvaco-Atlas simulator. In the first step of the work, a reference structure of FTO/i-SnO2/CdS/CdTe solar cell was studied and simulated based on experimental data for the validity of the simulation and the extent to which present results agree with the experimental data. An air mass 1.5 global spectrum (AM1.5G) with an incident irradiance of 1000 W/m2 was assumed during the simulations: the conversion efficiencies obtained are 13.96%. This simulation result is in good agreement with experimental data reported in the literature. In the second step, in order to optimize CdTe solar cell performances, a new structure is proposed by incorporation of a cuprous oxide (p-type Cu2O) layer at back-contact as a Hole transport-Electron blocking layer (HT-EBL), with the aim of minimizing the minority carrier recombination losses. High performance has been obtained by optimizing the cell parameters in terms of thickness, doping concentration and carrier lifetime. Using the optimal parameters on which the optimal structure depends, the efficiency of the structure is increased by 10.35% compared to the reference cell. The simulation results have a high conversion efficiency of 24.35%, with short-circuit current density of 27.59 mA/cm2, an open-circuit voltage of 1.03 V and a fill-factor of 85.83%. The simulated efficiency of 24.35% was obtained for the optimized structure of FTO/i-SnO2/CdS/CdTe/Cu2O at room temperature (300 K). The next step was to investigate the thicknesses of the high-resistivity transparent (HRT) layer and the use of i-ZnO as an alternative to i-SnO2 material. The results showed that SnO2 film is more effective than ZnO in the CdTe solar cell device. Finally, we study the influences of temperature on the optimized CdTe solar cell performance in the range 270-330 K. The simulation results have shown a linear decrease in the device’s efficiency with increasing temperature.