Abstract

The GaInP/GaAs tandem cell on GaAs substrate and InGaAsP/InGaAs tandem cell on InP substrate were grown separately by all-solid state molecular beam epitaxy (MBE). Room-temperature direct wafer bonding technique was employed to integrate the top tandem junction and bottom tandem junction to form a single stack, which avoided high-temperature or long annealing and resulted in an abrupt interface with low resistance and high optical transmission. Furthermore, high-vacuum environment prevented the bonding interface from contamination. An efficiency of 42.0% of the GaInP/GaAs/InGaAsP/InGaAs four-junction solar cell was obtained at 230-times concentration of AM1.5D.

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