Current–voltage and spectral-response characteristics of surface-activated-bonding-based InGaP/GaAs/Si hybrid triple-junction cells

We measured the current–voltage (I–V) and spectral-response characteristics of InGaP/GaAs/Si hybrid triple-junction cells that were fabricated by using surface-activated bonding methods. We found by spectral response measurements that the current generated in the Si-based bottom cell was lower than those in the top and middle cells under the conditions of an air mass of 1.5G and one sun. Furthermore we observed a discrepancy between the short-circuit current, which was obtained by subtracting the estimated contribution of Si ledges surrounding InGaP/GaAs mesas to the I–V characteristics, and the results of spectral response measurements. One possible model for explaining the discrepancy was discussed on the basis of the electrical coupling scheme between subcells. The intrinsic conversion efficiency of a 5 × 5 mm2 triple-junction cell was crudely estimated to be ~26% by compensating for the shadow loss as well as subtracting the contribution of Si ledges.