Numerical Simulation of InAs/GaAs Quantum well and Quantum dots solar cells

Abstract

In this dissertation, InAs/GaAs multi-quantum well and quantum dots solar cells were simulated by MATLAB and Silvaco Atlas, respectively. First, a p-i-n InAs/GaAs multi-quantum well solar cell was simulated by MATLAB. In addition to Drift-Diffusion model, the Schrödinger equation is also included. We found an increase in efficiency from 16.78% to 18.52%. This increase due to the increase in short circuit current. Second, a p-i-n InAs/GaAs quantum dots solar cell was simulated by Silvaco Atlas. The quantum dots are inserted inside intrinsic region. This structure based on a real fabricated solar cell. The simulation was divided onto ideal case and real case. In the ideal case, it was found that the increase of QDs layers has improved monolithically the solar cell performance while doping has no significant effect. In the ideal case, the best obtained efficiency was 43.05 % for 10-layers of QDs. However, this is not in agreement with experimental works. To reproduce the experimental QDSC J-V native defects with discrete levels and additional defects resulting from InAs/GaAs QDs layers were taken into account; the electron traps levels result from the arsenic atom excess or indium vacancies near the QDs and the valence tail states originate from the perturbation of lattice periodicity GaAs. The obtained efficiency in this condition was 9.4 % in agreement with experimental efficiency of 9.1%. Finally, this QDSC was improved through doping and the number of QDs layers. The optimum obtained efficiency was 11.29 % for 2-layers of QDs and a doping density of 1×1019𝑐𝑚−3. Finally, as all discussed above, all the simulation results in this dissertation have shown accuracy when comparing with experimental work. This dissertation helps build correct, complete models for both multi-quantum well solar cells and quantum dots solar cells. These obtained results can help to develop solar cells with high-efficiency, and why not help to develop new technology for this type of solar cell because the technology of quantum dots in our view did not developed enough to manufacture quantum dots solar cell with high efficiency. In this dissertation InAs/GaAs quantum solar cells is studied. First with a quantum well conception (QWSCs) and secondly with quantum dots (QDSCs). For the InAs/GaAs QW, we used MATLAB to develop our own program to solve consistently the classical drift-diffusion model with Schrödinger-Poisson model. The QWSC provided a cell efficiency of 18.52% compared with 16.78% for the classical one. The InAs/GaAs QDSC was studied using Silvaco Atlas simulator. The study is divided into two parts: ideal and real case. The effects of the number of quantum dots (QDs) layers and the doping of QDs on electrical properties of QDSC are investigated. A highest efficiency of 43.05 % was obtained in the ideal case. However experimental works have reported a conversion efficiency of 9.1%. Taking into account the presence of discrete electron traps and valence band tail, we were able to obtain a cell efficiency of 9.4% in agreement with experimental reports. In addition, it was possible to improve the cell efficiency to 11.29% by optimizing the number and the doping of QDs layers, to 2-layers and 1×1019𝑐𝑚−3, respectively.