| Summary: | 碩士 === 國立東華大學 === 電機工程學系 === 94 === The energy conversion efficiencies of traditional multi-junction solar cells (MJSCs) are limited by the current-mismatch between their subcells. To solve this problem, the application of the quantum well solar cells in MJSCs could achieve a better current-match and improve the energy conversion efficiencies of the traditional MJSCs.
In this thesis, a theoretical model to determine the quantum efficiency of quantum well solar cells is constructed. Additionally, the energy conversion efficiencies of multi-junction solar cells are calculated, and the device performance of MJSCs with the QWSC as the subcells is analyzed. To calculate the quantum efficiency of quantum well solar cell, first the photocurrents in the quasi-neutral p-, n-, and space charge regions are determined, and thus the total photon-generated current is obtained. Theoretical energy conversion efficiencies of solar cells are obtained from the illuminated current-voltage characteristics based on the principle of superposition.
With the incorporation of the quantum well solar cells in the multi-junction solar cells, we propose the device structures of dual-junction solar cells, a stack of a GaAs solar cell and a QWSC, and three-junction solar cells, a stack of a GaInP solar cells and two individual QWSC. By tuning the thickness of each subcell, the high short-circuit current density of the resulting multi-junction solar cells could be achieved. The energy conversion efficiency of 29.2% is predicted for the two-junction solar cells of InGaAsP/InGaAs QWSC series-connected with the GaAs p-n junction cells. Furthermore, through our estimation the energy conversion efficiency of three-junction solar cells consisting of the strain-balanced GaAsP/InGaAs QWSC, InGaAsP/InGaAs QWSC, and GaInP p-n cells could reaches as high as 35.8%.
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