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Published May 2006 | Published
Book Section - Chapter Open

Lattice-Mismatched Monolithic GAAS/INGAAS Two-Junction Solar Cells by Direct Wafer Bonding


Direct bonded interconnect between subcells of a lattice-mismatched III-V compound multijunction cell would enable dislocation-free active regions by confining the defect network needed for lattice mismatch accommodation to tunnel junction interfaces, while metamorphic growth inevitably results in less design flexibility and lower material quality than is desirable. The first direct-bond interconnected multijunction solar cell, a two-terminal monolithic GaAs/InGaAs two-junction solar cell, is reported and demonstrates viability of direct wafer bonding for solar cell applications. The tandem cell open-circuit voltage was approximately the sum of the subcell open-circuit voltages. This achievement shows direct bonding enables us to construct lattice-mismatched III-V multijunction solar cells and is extensible to an ultrahigh efficiency InGaP/GaAs/InGaAsP/InGaAs four-junction cell by bonding a GaAs-based lattice-matched InGaP/GaAs subcell and an InP-based lattice-matched InGaAsP/InGaAs subcell. The interfacial resistance experimentally obtained for bonded GaAs/InP smaller than 0.10 Ohm-cm^2 would result in a negligible decrease in overall cell efficiency of ~0.02%, under 1-sun illumination.

Additional Information

© 2006 IEEE. Issue Date: May 2006. Date of Current Version: 15 January 2007. This work was supported by NASA and the National Renewable Energy Laboratory. Alireza Ghaffari, Robert Walters of the California Institute of Technology and James Zahler of the Aonex Technologies are acknowledged for their technical support in development of the bonding process and the electrical measurements. One of the authors (KT) was supported in part by the Japanese ITO Scholarship for International Education Exchange.

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