A New Class Of High Efficiency, High Specific Power, Multi-junction Photovoltaic Cells Using Wafer Bonding And Layer Transfer

The objective of this proposal is to demonstrate the feasibility of a process for producing ultra-high conversion efficiency (37-41%) AM0 multijunction solar cells from dislocation-free non-lattice matched heterostructures using a proprietary wafer bonding / layer transfer process. The overall cell fabrication process will yield a two terminal, series-connected four junction InGaP/GaAs/InGaAsP/InGaAs/InP/Si solar cell. Specifically, as a proof of principle, we will transfer of Ge layers < 500 nm thick and 50 mm in diameter onto Si substrates, and then use the resulting Ge/Si substrates as epitaxial growth templates for high bandgap InGaP/GaAs tandem cells. We will also transfer < 500 nm thick InP layers and 50 mm diameter onto Si substrates and use the InP/Si substrates as epitaxial growth templates for low bandgap InGaAsP/InGaAs tandem cells. Device active region structure will be characterized via electron microscopy, X-ray diffraction, and minority carrier lifetime will be characterized via time-resolved photoluminescence. The dark and AM0-illuminated current-voltage characteristics of an InGaP/GaAs dual junction cell on Ge/Si templates will be determined. The results obtained will be used to estimate the overall four junction cell efficiency potential and guide development of a commercial prototype four junction cell process in Phase II.