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Published September 4, 2006 | Published
Journal Article Open

Direct-bonded GaAs/InGaAs tandem solar cell


A direct-bonded GaAs/InGaAs solar cell is demonstrated. The direct-bonded interconnect between subcells of this two-junction cell enables monolithic interconnection without threading dislocations and planar defects that typically arise during lattice-mismatched epitaxial heterostructure growth. The bonded interface is a metal-free n+GaAs/n+InP tunnel junction. The tandem cell open-circuit voltage is approximately the sum of the subcell open-circuit voltages. The internal quantum efficiency is 0.8 for the GaAs subcell compared to 0.9 for an unbonded GaAs subcell near the band gap energy and is 0.7 for both of the InGaAs subcell and an unbonded InGaAs subcell, with bonded and unbonded subcells similar in spectral response.

Additional Information

© 2006 American Institute of Physics (Received 19 March 2006; accepted 26 July 2006; published online 6 September 2006) The authors acknowledge Robert Reedy of the National Renewable Energy Laboratory for expert assistance with SIMS measurements. 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 (K.T.) was supported in part by the Japanese ITO Scholarship for International Education Exchange.

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