Wafer-bonded two-terminal III-V//Si triple-junction solar cell with power conversion efficiency of 36.1% at AM1.5g

In this work, we present the fabrication and analysis of a wafer-bonded GaInP/GaInAsP//Si triple-junction solar cell with 36.1% conversion efficiency under AM1.5g spectral illumination. The new cell design presents an improvement over previous III-V//Si triple-junction cells by the implementation of a rear-heterojunction for the middle cell. Furthermore, an advanced metallodielectric rear-side grating was used for light trapping enhancement in the silicon bottom cell that increased the silicon subcell current by 1.4 mA/cm2. The external radiative efficiency was quantified to be 1.5 times higher compared to a reference device with a GaInAsP homojunction middle cell. A luminescent coupling factor of 0.46 between the middle and bottom subcell was determined. The share of recombination in the space-charge region was experimentally shown to be insignificant as intended by the rear-heterojunction design. Overall, the open-circuit voltage of the middle cell increased by 61 mV compared to the previous generation. Given the established long-term stability of III-V and silicon-based solar cells, these results are promising steps towards the future employment of III-V/Si tandem solar cells.