Elaboration, Characterizations and Modeling of Photovoltaic Structures Based on III-V Materials

Abstract

In this thesis, we presented a study for modeling and developing solar cells. It is believed that it will be of great value to the developers and photovoltaic industry. Since almost all research on advanced solar cells is currently conducted via expensive and complex experimentation, the proposed simulation method is expected to help reduce that cost, simplify the design process, and allow the designer to focus on the final result. The main topic of this Ph.D. research is to describe the simulation methodology and simulation results of a lattice-matched InGaP/GaAs/Ge triple-junction solar cell, including the development of monolithically stacking technology of the sub-cells and their interconnections; understanding and predicting the performance of the Monolithically Multi-Junction (MMJ) solar cells through numerical simulation of the optical, electrical characteristics of the cell. Multi-junction solar cells based on III-V materials have achieved the highest efficiencies of any present photovoltaic technology. The work presented in this thesis concerns of study and modeling of photovoltaic structures based on III-V Materials. In this thesis, our successful effort in modeling and optimization of higher efficiency InGaP/GaAs/Ge monolithically triple-junction solar cell is investigated, in order to understand and predict the performance of the MMJ solar cells, Mechanically Stacked Multi-Junction (MSMJ) solar cell was simulated first. Very high performance III-V single-junction solar cells have been demonstrated, with the best efficiencies of 18.55% for InGaP, 29.39% for GaAs and 7.11% for Ge respectively under 1-sun (AM1.5G spectrum) illumination used for terrestrial applications. After the demonstration of individual sub-cells, mechanically and monolithically stacked for GaAs/Ge dual-junction cells and InGaP/GaAs/Ge triple junction cells are demonstrated as well. The efficiency of 33.28% for GaAs/Ge dual-junction solar cell, while 35.54% for InGaP/GaAs/Ge triple-junction solar cell under AM1.5G spectrum to illumination are realized with minimal effort and cost. Silvaco provides a modeling program called ATLAS that is specifically designed to model semiconductor devices. Silvaco ATLAS is the software used in this thesis to simulate the performance of solar cells. ATLAS was used to model III-V multi-junction solar cells that are currently being produced to verify the validity of the model. This work aims to supplement and ground the experimental undertakings with a strong theoretical basis. This is accomplished by numerical calculations based on the detailed model and by physics based device simulation. Our simulation results suggest an optimistic future for integrating III-V solar cell technology and will be useful for future design and prediction of multi-junction III-V solar cell performance.