High-performance GaAsP/SiGe solar cell on silicon

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Copyright: Diaz, Martin
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Abstract
Crystalline silicon remains the dominant technology of the existing commercial solar energy market as the cost of silicon continues to decrease. However, despite the abundance and low cost of silicon, the progress of single-junction silicon solar cell efficiency has stagnated. To further reduce the levelized cost of energy higher efficiency must be achieved. In contrast, III-V based solar cells have steadily improved in performance over recent years while also reaching the highest efficiencies reported with multi-junction devices. The integration of high-performance III-V multi-junction and silicon based technologies is the next step for achieving high-efficiency solar cells at lower cost. This research accomplishes the merging of these two technologies while demonstrating high efficiencies rivaling current III-V on silicon technology. The approach used in this work utilizes a metamorphic silicon germanium buffer layer between the silicon platform and the epitaxial grown device layers. The result is a lattice-matched GaAsP/SiGe dual-junction solar cell device on a silicon substrate with a low dislocation interface between the silicon substrate and the active device layers. This device structure is achieved using a two-step growth process on silicon. The SiGe graded buffer layer and SiGe bottom cell is first grown using reduced pressure chemical vapor deposition followed by the growth of the III-V top cell layers using metal organic chemical vapor deposition. The fabrication of two-terminal dual-junction GaAsP/SiGe on silicon devices is carried out primarily with the process of photolithography. Through development and design improvements to this tandem solar cell device structure an efficiency of 18.9% under 1-sun is demonstrated. This device exhibits a JSC of 18.1 mA/cm2, a VOC of 1.45 V, and a FF of 72%. Analysis shows that the device is currently limited by the SiGe bottom cell and high series resistance lowering the fill factor. The existing limitations of this structure are addressed along with a pathway to the predicted 1-sun practical efficiency of 32.5%.
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Author(s)
Diaz, Martin
Supervisor(s)
Barnett, Allen
Perez-Wurfl, Ivan
Opila, Robert
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Publication Year
2017
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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